Fix test_sql pytest fixture warnings
- [y] closes #22338
- [y] tests added / passed
- [y] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

See Travis CI Python 3.6 build [before](https://travis-ci.org/pandas-dev/pandas/jobs/419432794) and [after](https://travis-ci.org/pandas-dev/pandas/jobs/420824121) my changes get rid of the warning for calling fixtures directly.

You can see this by searching for the string "pandas/tests/io/test_sql.py" to see that well over 100 warnings have been removed.
Hello @alimcmaster1! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on August 31, 2018 at 17:49 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22515?src=pr&el=h1) Report
> Merging [#22515](https://codecov.io/gh/pandas-dev/pandas/pull/22515?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/14ccdd22f158b7944a403e02082402bc85fb11a5?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22515/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22515?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #22515   +/-   ##
=======================================
  Coverage   92.04%   92.04%           
=======================================
  Files         169      169           
  Lines       50782    50782           
=======================================
  Hits        46744    46744           
  Misses       4038     4038
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.45% <ø> (ø)` | :arrow_up: |
| #single | `42.26% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22515?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22515?src=pr&el=footer). Last update [14ccdd2...7427924](https://codecov.io/gh/pandas-dev/pandas/pull/22515?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 See Travis CI Python 3.6 build [before](https://travis-ci.org/pandas-dev/pandas/jobs/419432794) and [after](https://travis-ci.org/pandas-dev/pandas/jobs/420824121)  my changes this get rid of the warning for calling fixtures directly. https://travis-ci.org/pandas-dev/pandas/jobs/421777999#L2544

@jreback : Not sure why `scipy` is breaking on these builds suddenly...did something happen to the `2.7` package for `scipy` ? Close/Re-open to restart CI after SciPy failures  @alimcmaster1: feel to also ping us if you want to restart one of your builds so that you don't have to retrigger the entire test suite. Thanks @gfyoung will do that in the future! Thanks @WillAyd for reviewing this. I've update to get rid of the final warning for this file. See travis 3.6 [build](https://travis-ci.org/pandas-dev/pandas/jobs/425438724) now is warning free for this file :) This looks good to me. Let's merge so we can make progress on getting our CI in shape again.