Remove duplicate LLVM_NATIVE_ from llvm's config.h

Summary:
Since LLVM_NATIVE_ARCH, LLVM_NATIVE_ASMPARSER, LLVM_NATIVE_ASMPRINTER,
LLVM_NATIVE_DISASSEMBLER, LLVM_NATIVE_TARGET, LLVM_NATIVE_TARGETINFO and
LLVM_NATIVE_TARGETMC are already defined in llvm-config.h, there seems
to be no reason to also define them in config.h.  Also, I can only find
usage of these macros in files that include llvm-config.h.

So let's remove the duplicated macros from config.h.

Reviewers: chandlerc, rnk, mehdi_amini, joerg

Reviewed By: rnk

Subscribers: chapuni, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D33881

llvm-svn: 304714