Build: remove non-existing README files from Makefile.am
    
    Some Makefile.am files were apparently created by copy-pasting other
    files. As a result, some Makefiles require non-existing README files.
    Remove this to fix dist target.
    
    https://fedorahosted.org/freeipa/ticket/6418
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>