[clang] Remove unit test which uses reverse-iterate flag

Summary: This patch is in response to https://reviews.llvm.org/D35043 which removed -reverse-iterate flag.

Reviewers: dblaikie, mehdi_amini

Reviewed By: dblaikie

Subscribers: cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D36386

llvm-svn: 311720