astro/astrometry: Put python into versioned dir

The Python files and libraries were incorrectly installed under
lib/python instead of lib/python3.x and were therefore not version
specific. This was corrected by using PYTHON_LIBDIR.

While here, doing some more corrections:

• Use PY_BASE_INSTALL_DIR for PYTHON_LIBDIR
• Move DATA_INSTALL_DIR into MAKE_ENV
• Strip bin and lib files
• Remove PORTDOCS and PORTEXAMPLES entries
• Pet portclippy
• Update pkg-plist
• Bump PORTREVISION

MFH: 2022Q3