in tests, change pd.arrays.SparseArray to SparseArray
- [x] closes https://github.com/pandas-dev/pandas/pull/30656#discussion_r363060184
- [x] tests added / passed
    - modified most tests that use `pd.arrays.SparseArray` to just import `SparseArray`
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
    - N/A

For @jreback to review based on his comment previous PR #30656 

In a few files (see below), left it as is because usage was pretty local (and allows `pd.arrays.SparseArray` reference to be tested in code)
```bash
$ grep -c -r arrays.SparseArray . | grep -v ":0"
./dtypes/test_generic.py:1
./frame/methods/test_quantile.py:2
./series/test_missing.py:2
```



My style preference is to just use `pd.arrays` namespace. > My style preference is to just use `pd.arrays` namespace.

So in the various test modules, 
So @TomAugspurger prefers to use `pd.arrays.SparseArray`, i.e., writing `pd.arrays.SparseArray([1,2,3])` in a test.
And @jreback prefers to `from pd.arrays import SparseArray`, i.e., writing `SparseArray([1,2,3])` in a test

I did the latter because of feedback from @jreback , so you guys need to work out your differences.
 Yep, that's what we're doing.

On Tue, Jan 7, 2020 at 3:00 PM Irv Lustig <notifications@github.com> wrote:

> My style preference is to just use pd.arrays namespace.
>
> So in the various test modules,
> So @TomAugspurger <https://github.com/TomAugspurger> prefers to use
> pd.arrays.SparseArray, i.e., writing pd.arrays.SparseArray([1,2,3]) in a
> test.
> And @jreback <https://github.com/jreback> prefers to from pd.arrays
> import SparseArray, i.e., writing SparseArray([1,2,3]) in a test
>
> I did the latter because of feedback from @jreback
> <https://github.com/jreback> , so you guys need to work out your
> differences.
>
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 this looks fine to me, i slightly prefer the shorter syntax. unless @TomAugspurger objects, ok to merge this. No objections. 

> On Jan 7, 2020, at 17:13, Jeff Reback <notifications@github.com> wrote:
> 
> ﻿
> this looks fine to me, i slightly prefer the shorter syntax. unless @TomAugspurger objects, ok to merge this.
> 
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