swift234

[test] Add type annotations to Set.swift test.

Previously, these functions each took over a second to type-check on my
machine; now they're all below one second, and one unused function has
been deleted outright. (-Wunused, anyone?)

I filed rdar://problem/19181998 for one strange case, but this is mostly
just the usual "type-checker is slow and tries too many things".

Swift SVN r23790