swift234

First steps at simplifying generic specializer interface.

This change removes some of the bucketing that was happening as part of
generic specialization. Now that we can properly mangle the specialized
function names and look up the previously specialized functions, this is
not necessary.

I verified that stdlib build times do not get longer with this change,
and that the generated SIL is virtually the same (virtually because we
have some non-determinism in our build at the moment:
rdar://problem/20304012).

Swift SVN r26754