Now that we have two connections to the X server, the idea of a
ref-counted server grab that might be held across extended portions
of code is very dangerous since we might try to use the backend
connection while the frontend connection is grabbed.
Replace the only usage (which was local) with direct
XGrabServer/XUngrabServer usage and remove the meta_display_grab()
API.
https://bugzilla.gnome.org/show_bug.cgi?id=733068