console: Only use basic GJS API <gjs/gjs.h> and link against GLib

We need to link explicitly against GObject, since we use The
commit 25681375 intentionally removed the dependency on all
the "internal" GJS libraries like libmozjs.so from gjs-console,
but first, we need to explicitly link against libgobject, because
we do use it.

Secondly, to make things more clear here, drop the random unnecessary
use of "internal" GJS API like gjs_debug and gjs_memory_report (
the memory report could be an environment variable).

https://bugzilla.gnome.org/show_bug.cgi?id=632844