Completely strip shebangs from Python files that will be installed to /usr/share/
    
    In the source directory, currently, all Python files under ./bleachbit/
    get installed to /usr/share/ as non-executable files, so they don't
    require a shebang at all. I don't know if this is guaranteed, though, so
    this may or may not need a better heuristic later.
    
    In the source, for some reason, most Python files have the executability
    bit, which is then removed where unneeded during `make`. So, what seems
    more foolproof would be to wait till after %build and %install, test
    files installed under /usr/share/bleachbit/ for executability, and
    *then* remove the unneeded shebangs... But this causes a timestamp
    mismatch between the source files and compiled byte code, which will
    force the Python interpreter to recompile every time.