drm/vram: drop DRM_VRAM_MM_FILE_OPERATIONS

Not needed any more because we don't have vram specific fops
any more.  DEFINE_DRM_GEM_FOPS() can be used instead.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20191016115203.20095-12-kraxel@redhat.com