TST/CLN: deduplicate fixture from test_to_latex.py
this PR is basically just to promote the float_frame fixture to top-level conftest.

once there, there is opportunities to re-use by fixturising current instances of 

```
df = DataFrame(tm.getSeriesData())
```

also allows removing duplicate fixture from pandas/tests/io/formats/test_to_latex.py

so this is just a move for now, fixturization in follow-on PRs
lgtm. CI failing on doc build, so will merge after that is disabled. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26603?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@437efa6`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26603/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26603?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #26603   +/-   ##
=========================================
  Coverage          ?   91.84%           
=========================================
  Files             ?      174           
  Lines             ?    50707           
  Branches          ?        0           
=========================================
  Hits              ?    46574           
  Misses            ?     4133           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.38% <ø> (?)` | |
| #single | `41.76% <ø> (?)` | |


------

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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26603?src=pr&el=footer). Last update [437efa6...3b3c0f0](https://codecov.io/gh/pandas-dev/pandas/pull/26603?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 i think i accidentally cancellled this one
can u merge master and ping on green @jreback all green Thanks @simonjayhawkins 