lib: simplify version; drop get_current_revision - it was run every time on import time - we don't want that

This functionality was already not in use with the version numbers we use. I
also doubt it is possible to have version numbers where it worked - it seems
like there might have been some regression that nobody noticed. Dropping it
will thus not really lose any actual functionality.

If we want to include the revision number in the version (for browser cache
invalidation) then we should do it in a different way. Perhaps writing it to
some file from setup.py .