[Python] Remove the deprecated pyarrow.filesystem legacy implementations #20127

The pyarrow.filesystem and pyarrow.hdfs filesystems have been deprecated in 2.0.0, and changed from Deprecation to FutureWarning in 4.0.0. I think it is time to actually remove them, and I would propose to do so in 8.0.0

Reporter: Joris Van den Bossche / @jorisvandenbossche

Related issues:

• [Python] Remove the legacy ParquetDataset custom python-based implementation (is blocked by)

_{Note: This issue was originally created as ARROW-15761. Please see the migration documentation for further details.}