Remove the unuseful -fdiagnostics-show-name

This option was added in r129614 and doesn't have any use case that I'm aware
of. It's possible that external tools are using these names - and if that's
the case we can certainly reassess the functionality, but for now it lets us
shave out a few unneeded bits from clang.

Move the "StaticDiagNameIndex" table into the only remaining consumer, diagtool.
This removes the actual diagnostic name strings from clang entirely.

Reviewed by Chris Lattner & Ted Kremenek.

llvm-svn: 150612