Remove the static initialize introduced in r365099

Summary:
Some polish for r365099 which adds a static initializer to
MachOObjectFile. Remove it by moving it to file scope.

Reviewers: smeenai, alexshap, compnerd, mtrent, anushabasana

Reviewed By: smeenai

Subscribers: hiraditya, jkorous, dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64873

llvm-svn: 366496