Drop unused readline import
    
    The actual readline usage was removed in commit f19218f7
    (Remove duplicate and unused utility code,
    https://fedorahosted.org/freeipa/ticket/2650) and the import remained.
    
    Readline should not be initialized if the output is not to terminal (and it
    does no checks itself, so import in anything that would be useful to redirect
    should be conditional), since it may garble the output [1]:
    
    $ TERM=xterm python -c 'import readline' |hexdump -C
    00000000  1b 5b 3f 31 30 33 34 68                           |.[?1034h|
    00000008
    
    [1] https://bugzilla.redhat.com/show_bug.cgi?id=304181#c1
    
    https://fedorahosted.org/freeipa/ticket/2691
    https://fedorahosted.org/freeipa/ticket/3276