Revert "[XRay][AArch64] An attempt to fix test patching-unpatching.cc by...

Revert "[XRay][AArch64] An attempt to fix test patching-unpatching.cc by flushing the instruction cache after code modification"

This reverts commit r290354, as it broke the build. We need to make sure
this builds on AArch64 before committing again.

llvm-svn: 290362