arrow

GH-31303: [Python] Remove the legacy ParquetDataset custom python-based implementation (#39112)

### Rationale for this change

Legacy ParquetDataset has been deprecated for a while now, see
https://github.com/apache/arrow/issues/31529. This PR is removing the
legacy implementation from the code.

### What changes are included in this PR?

The PR is removing:
- `ParquetDatasetPiece `
-  `ParquetManifest`
-  `_ParquetDatasetMetadata `
-  `ParquetDataset`

The PR is renaming `_ParquetDatasetV2` to `ParquetDataset` which was
removed. It is also updating the docstrings.

The PR is updating:
- `read_table`
-  `write_to_dataset`

The PR is updating all the tests to not use `use_legacy_dataset` keyword
or legacy parametrisation.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

Deprecated code is removed.
* Closes: #31303