Remove "Quit" from shortcuts page

Hi,

I've got a report at downstream bugzilla that shortcut "Ctrl + q" does not do anything although it is listed at shortcuts page for "Quit". I couldn't find it working in older releases too so I think that it should not be mentioned at the shortcuts page at all.

Additional details: https://bugzilla.redhat.com/show_bug.cgi?id=2006768