x11-terms/gnome-terminal: remove some unnecessary USE requirements on dependencies

x11-terms/gnome-terminal: remove some unnecessary USE requirements on dependencies

dev-libs/glib[dbus] just pulls in dconf at runtime, but we already have that
dependency here explicitly ourselves; no need to force a rebuild of glib just
for that then.

gtk+[X] is not required and a build against a pure-wayland gtk+ should work
just fine. The problem is that it won't grow X11 support after gtk+ is rebuilt
with USE=X and gnome-terminal not rebuilt. But it'll work fine, just have some
X11 specific extra cases or features disabled. Or it will break if USE=X is
initially there on gtk+, but later removed.
This is a global issue in gtk+[X,wayland] handling and we shouldn't disallow
pure wayland gnome-terminal builds in the meantime. Bug 624960 tracks the
global concerns.

Package-Manager: Portage-2.3.19, Repoman-2.3.6