Remove "localize global" optimization

Summary:
As discussed in http://llvm-reviews.chandlerc.com/D1754,
this optimization isn't really valid for C, and fires too rarely anyway.

Reviewers: rafael, nicholas

Reviewed By: nicholas

CC: rnk, llvm-commits, nicholas

Differential Revision: http://llvm-reviews.chandlerc.com/D1769

llvm-svn: 191834