feat: Update to XRootD v5.4.1 (!64)

Resolves #23 (closed)

* Update to XRootD v5.4.1 for modern setuptools support.
   - c.f. https://github.com/xrootd/xrootd/releases/tag/v5.4.1
* This takes advantage of the following PRs for support for modern
setuptools support in Python 3.
   - https://github.com/xrootd/xrootd/pull/1585
   - https://github.com/xrootd/xrootd/pull/1586
   - https://github.com/xrootd/xrootd/pull/1605
   - https://github.com/xrootd/xrootd/pull/1623
* Use PIP_VERBOSE CMake option to have better logging of Python bindings install.
* Remove PYTHONPATH manipulation.
   - Effectively reverts MR !58