Zap the Sema constant initializer checking code that we aren't using

Zap the Sema constant initializer checking code that we aren't using
anymore.  If we want to reuse bits and pieces to add strict checking for
constant initializers, we can dig them out of SVN history; the existing
code won't be useful as-is.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@65502 91177308-0d34-0410-b5e6-96231b3b80d8