STYLE, TYP frame-or-series-union check no longer relevant
This check is no longer relevant:

https://github.com/pandas-dev/pandas/blob/9ab55b4aed9018b070c939ffbdf232f99bf50f1a/.pre-commit-config.yaml#L83-L88

Since using PEP604 rewrites, this would be written as
```
x: Series | DataFrame
```
anyway.
```
x: FrameOrSeriesUnion
```
is actually just as long as the above, and arguably less explicit.

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@simonjayhawkins thoughts on replacing all the `FrameOrSeriesUnion` occurrences, removing the alias, and removing the above check?