[HWASan] remove replacement of DbgVariableIntrinsics.

This code was dead because we AI->replaceUsesWithIf above. I verified
this doesn't actually get run by applying
https://gist.github.com/fmayer/aea7cbb4700cfe2c9d932591ae1073c3 to the
Android toolchain and building AOSP, without any crash.

Reviewed By: eugenis

Differential Revision: https://reviews.llvm.org/D119802