[msan] Remove MSanDR and supporting code.

MSanDR is a dynamic instrumentation tool that can instrument the code
(prebuilt libraries and such) that could not be instrumented at compile time.

This code is unused (to the best of our knowledge) and unmaintained, and
starting to bit-rot.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@222232 91177308-0d34-0410-b5e6-96231b3b80d8