STYLE #49656: fixed redefined-outer-name linting issue to format.py 
Fixed redefined-outer-name issue in:
- pandas/io/formats/format.py

redefined-outer-name t issues raised for:
- justify function (import from pandas.io.formats.printing)
- decimal (changed to from decimal import Decimal) 
- is_dates_only parameter conflict with function name 
- updated get_format_datetime64 function with renamed parameter

- passed related tests in pytest pandas
- running:  pylint --disable=all --enable=redefined-outer-name pandas/io/
-- > Results in 10.00/10 rating


Thanks @MarieKMiko 