drm: drop DRM_AUTH from PRIME_TO/FROM_HANDLE ioctls

As mentioned by Christian, for drivers which support only primary nodes
this changes the returned error from -EACCES into -EOPNOTSUPP/-ENOSYS.

For others, this check in particular will be a noop. So let's remove it
as suggested by Christian.

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sean Paul <sean@poorly.run>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20191101130313.8862-5-emil.l.velikov@gmail.com