MAINTAINERS: remove METAG imgdafs pattern

This never made it into the kernel tree.  Remove it.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>