Remove NaClX86_64TargetCodeGenInfo and NaClARMTargetCodeGenInfo

Summary:
They just existed before to use NaCl's custom ABIInfos; now that those are gone,
the custom TargetCodeGenInfos are no longer needed either.

Test Plan: don't break the existing tests

Reviewers: jvoung

Subscribers: jfb, cfe-commits

Differential Revision: http://reviews.llvm.org/D7234

llvm-svn: 227406