DOC: Updated doc-string using new doc-string design for DataFrameFormatter
`DataFrameFormatter` does not have this parameter: `force_unicode_docstring`. This change uses the doc-string re-design in #11011 

what is this supposed to address?
 Redundant parameter in docstring
 So the original docstring for DataFrameFormatter is not correct(one or two more parameters in docstring but not in the function declaration). This PR fixed that. Can you merge? 
 post the original and the new 
 ```
common_docstring = """
    Parameters
    ----------
    buf : StringIO-like, optional
        buffer to write to
    columns : sequence, optional
        the subset of columns to write; default None writes all columns
    col_space : int, optional
        the minimum width of each column
    header : bool, optional
        whether to print column labels, default True
    index : bool, optional
        whether to print index (row) labels, default True
    na_rep : string, optional
        string representation of NAN to use, default 'NaN'
    formatters : list or dict of one-parameter functions, optional
        formatter functions to apply to columns' elements by position or name,
        default None. The result of each function must be a unicode string.
        List must be of length equal to the number of columns.
    float_format : one-parameter function, optional
        formatter function to apply to columns' elements if they are floats,
        default None. The result of this function must be a unicode string.
    sparsify : bool, optional
        Set to False for a DataFrame with a hierarchical index to print every
        multiindex key at each row, default True
    index_names : bool, optional
        Prints the names of the indexes, default True"""

justify_docstring  = """
    justify : {'left', 'right'}, default None
        Left or right-justify the column labels. If None uses the option from
        the print configuration (controlled by set_option), 'right' out
        of the box."""

force_unicode_docstring = """
    force_unicode : bool, default False
        Always return a unicode result. Deprecated in v0.10.0 as string
        formatting is now rendered to unicode by default."""

return_docstring = """

    Returns
    -------
    formatted : string (or unicode, depending on data and options)"""
```

The original is the sum of all the above 

```
docstring_to_string = common_docstring + justify_docstring + force_unicode_docstring + return_docstring
```

The new one is

```
common_docstring + justify_docstring + return_docstring
```

or the original one excluding `force_unicode_docstring`
 i am excluding it since this function/class does not have `force_unicode_docstring` to be passed in
 I can read the code
I want to see what it looks like under 0.16.2 thrn after this change is applied 
 I am not sure what you mean but just to better clarify this: This PR only excludes/removes one parameter from the docstring of `DataFrameFormatter` since `DataFrameFormatter` does not have `force_unicode_docstring` as a parameter.
 post what the doc string looks like before and after the change
 The original: 

```
    Parameters
    ----------
    buf : StringIO-like, optional
        buffer to write to
    columns : sequence, optional
        the subset of columns to write; default None writes all columns
    col_space : int, optional
        the minimum width of each column
    header : bool, optional
        whether to print column labels, default True
    index : bool, optional
        whether to print index (row) labels, default True
    na_rep : string, optional
        string representation of NAN to use, default 'NaN'
    formatters : list or dict of one-parameter functions, optional
        formatter functions to apply to columns' elements by position or name,
        default None. The result of each function must be a unicode string.
        List must be of length equal to the number of columns.
    float_format : one-parameter function, optional
        formatter function to apply to columns' elements if they are floats,
        default None. The result of this function must be a unicode string.
    sparsify : bool, optional
        Set to False for a DataFrame with a hierarchical index to print every
        multiindex key at each row, default True
    index_names : bool, optional
        Prints the names of the indexes, default True
    justify : {'left', 'right'}, default None
        Left or right-justify the column labels. If None uses the option from
        the print configuration (controlled by set_option), 'right' out
        of the box.
    force_unicode : bool, default False
        Always return a unicode result. Deprecated in v0.10.0 as string
        formatting is now rendered to unicode by default.

    Returns
    -------
    formatted : string (or unicode, depending on data and options)
```

The new one:

```
    Parameters
    ----------
    buf : StringIO-like, optional
        buffer to write to
    columns : sequence, optional
        the subset of columns to write; default None writes all columns
    col_space : int, optional
        the minimum width of each column
    header : bool, optional
        whether to print column labels, default True
    index : bool, optional
        whether to print index (row) labels, default True
    na_rep : string, optional
        string representation of NAN to use, default 'NaN'
    formatters : list or dict of one-parameter functions, optional
        formatter functions to apply to columns' elements by position or name,
        default None. The result of each function must be a unicode string.
        List must be of length equal to the number of columns.
    float_format : one-parameter function, optional
        formatter function to apply to columns' elements if they are floats,
        default None. The result of this function must be a unicode string.
    sparsify : bool, optional
        Set to False for a DataFrame with a hierarchical index to print every
        multiindex key at each row, default True
    index_names : bool, optional
        Prints the names of the indexes, default True
    justify : {'left', 'right'}, default None
        Left or right-justify the column labels. If None uses the option from
        the print configuration (controlled by set_option), 'right' out
        of the box.

    Returns
    -------
    formatted : string (or unicode, depending on data and options)
```
 hmm, I think we can take that `force_unicode` out entirely, it was removed in 0.14.0
 Okay I'll take it out.
 No wonder i don't see any usage of `force_unicode` when PR #11011 for `to_html`, `to_latex`, etc. I'll make the changes on those doc-strings too. 
 perfect ping when green
 @jreback  On green now. Thanks.
 thanks!
