TST/CLN: use float_frame fixture to remove use of tm.getSeriesData()
this PR removes 2 unnecessary fixtures from `pandas\tests\groupby\conftest.py`
 
and a few small changes to remove use of `tm.getSeriesData()` with a couple of exceptions:

- conftest files: `pandas\conftest.py` and `pandas\tests\frame\conftest.py` (needed for fixtures)
- `pandas\tests\frame\common.py` (this module will be removed on completion of #22471)
- `pandas\tests\io\json\test_pandas.py` (would benefit from fixturisation and access to other frame fixtures, separate PR and then maybe have a code-checks rule for `getSeriesData` in `test_*.py` files)

Makes sense to me # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26787?src=pr&el=h1) Report
> Merging [#26787](https://codecov.io/gh/pandas-dev/pandas/pull/26787?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ea06f8d1157601b5fdb48598e27b02149828fba0?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26787/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26787?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26787      +/-   ##
==========================================
- Coverage   91.72%   91.72%   -0.01%     
==========================================
  Files         178      178              
  Lines       50779    50779              
==========================================
- Hits        46579    46575       -4     
- Misses       4200     4204       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.31% <ø> (ø)` | :arrow_up: |
| #single | `41.18% <ø> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26787?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26787/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `78.94% <0%> (-10.53%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26787/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.88% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26787?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/26787?src=pr&el=footer). Last update [ea06f8d...a94a46e](https://codecov.io/gh/pandas-dev/pandas/pull/26787?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26787?src=pr&el=h1) Report
> Merging [#26787](https://codecov.io/gh/pandas-dev/pandas/pull/26787?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ea06f8d1157601b5fdb48598e27b02149828fba0?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26787/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26787?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26787      +/-   ##
==========================================
- Coverage   91.72%   91.72%   -0.01%     
==========================================
  Files         178      178              
  Lines       50779    50779              
==========================================
- Hits        46579    46575       -4     
- Misses       4200     4204       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.31% <ø> (ø)` | :arrow_up: |
| #single | `41.18% <ø> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26787?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26787/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `78.94% <0%> (-10.53%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26787/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.88% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26787?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/26787?src=pr&el=footer). Last update [ea06f8d...a94a46e](https://codecov.io/gh/pandas-dev/pandas/pull/26787?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @simonjayhawkins 