Move the KMS interaction from cogl into mutter, where most of the other
KMS interaction already takes place. This also removes dead code which
were only excercised when non-mutter callers used the cogl KMS backend.
The cogl KMS API was updated to pass via MetaRendererNative instead of
via the different cogl objects.
https://bugzilla.gnome.org/show_bug.cgi?id=768976