Drop .py extension from contrib/hooks/multimail/git_multimail.py
    
    Fedora 28 prints a deprecation notice if /usr/bin/python is called in an
    rpm build¹, which is done by default when byte-compiling python files
    outside of %{_libdir}/pythonX.X.
    
    Avoid the issue by dropping the .py extension from the multimail hook
    script.  The hook script is not used as a module and therefore has no
    need to use the extension or be byte-compiled.
    
    ¹ https://fedoraproject.org/wiki/Changes/Avoid_usr_bin_python_in_RPM_Build