The prefix, if any, of a variable name often contains information about
the namespace (such as clutter_backend is the ClutterBackend, while
backend is a MetaBackend). Clean up some more inconsistencies in
meta-renderer-native.c where various variable names were egl_ prefixed
but in fact was Cogl types.
https://bugzilla.gnome.org/show_bug.cgi?id=785381
7e1f65405f