drm: Nuke legacy maps debugfs files

GEM stopped using those a while ago, and no one should ever
need to use them again to debug legacy horror show drivers.

Nuke it all. Aside: It would kinda be nice if we'd have some
generic debugfs dumps for at least kms ...

Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1465930269-7883-2-git-send-email-daniel.vetter@ffwll.ch