swift234

Don't look in the parent metadata fields of structs and enums for
fulfillments, because we don't actually fill them in.

This is a minimal, temporary, speculative fix for the failure
described in rdar://25069637, for which I unfortunately do not have
a minimal test case and which I have been unable to duplicate in
my own testing due to various language restrictions that I hope
to lift given the better (but temporarily reverted) fix.