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ARROW-17891: [Docs][Python] Update and sync Win section of the developers/python page (#14350)

This PR updates Windows section of the Python Development page. Main changes:

- use Python 3.10 (also in instructions for Linux/MacOs)
- definition of `PATH` not needed as Python doesn't search in `PATH` for dlls anymore ([3.8 +](https://bugs.python.org/issue43173))
- use `CONDA_PREFIX` to define `ARROW_HOME` as in other parts of the docs
- remove **Running C++ unit tests for Python integration** section (C++ unit tests are part of `pytest`-based test module as of https://github.com/apache/arrow/pull/14117)

cc @wjones127 @jorisvandenbossche 

Authored-by: Alenka Frim <frim.alenka@gmail.com>
Signed-off-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>