lib/types: Revert handling submodules for "either"

This reverts commit 0f0805b5

, because @nbp had concerns about whether
this would be a good idea and pointed out problems with this.

We currently do not have a case where "either" is used in conjunction
with submodules, but I'm reverting it anyway to prevent people from
adding options using that type in that way.

This is now being reviewed in #14053.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>