[LLVM] Remove unwanted --check-prefix=CHECK from unit tests. NFC.

Summary: Removed unwanted --check-prefix=CHECK from numerous unit tests.

Reviewers: t.p.northover, dblaikie, uweigand, MatzeB, tstellarAMD, mcrosier

Subscribers: mcrosier, dsanders

Differential Revision: http://reviews.llvm.org/D19279

llvm-svn: 266834