swift234

Another improvement to 'class func' devirtualization.

Directly devirtualize cases where we can prove the method being invoked
is 'final'.

Previously we were able to do direct devirtualization (as opposed to
speculative) only when we could prove we knew the dynamic
type (e.g. through seeing a metatype instruction).

The code removed from isKnownFinal here was a vestige of previous
mechanical refactoring which made apparent the fact that this case was
not previously being handled.

There were some cases where the speculative devirtualzation code was
also able to prove there was only one alternative, but we really want
cases like this handled through direct devirtualization. It's possible
that the speculative devirtualization code that was catching some cases
like this is no longer useful and could be removed.

Swift SVN r26221