swift234

Unify the places where we simplify a conversion according
to a conversion restriction.

I'm pretty certain that this is *supposed* to be NFC, in that
any subtle differences between the two blocks are actually
inadvertent bugs.
Unify the two places that switch out on a conversion
restriction; I'm pretty sure they're supposed to be doing
the exact same thing, and that any differences between
flags/subFlags and whether to log the restriction kind
are inadvertent.

Swift SVN r14794