Bitcode: Remove reader support for MODULE_CODE_PURGEVALS.

Support for writing this module code was removed in r73220, which was well
before the LLVM 3.0 release, so we do not need to be able to understand it
for backwards compatibility.

Differential Revision: https://reviews.llvm.org/D31563

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@299370 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed