module.h: remove extable.h include now users have migrated

With hopefully most/all users of module.h that were looking for
exception table functions moved over to the new extable.h header,
we can remove the back-compat include that let us transition
without introducing build regressions.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Jessica Yu <jeyu@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>