drm/udl: Remove udl_fb.c

The remaining code in udl_fb.c is unused. Remove the file entirely.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191210084905.5570-10-tzimmermann@suse.de