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)
