Revert r230314, "Fix codegen for virtual methods that are (re-) exported from multiple modules."

It crashes for targeting (i686|x86_64)-win32.

  clang: clang/lib/AST/VTableBuilder.cpp:142: {anonymous}::FinalOverriders::OverriderInfo {anonymous}::FinalOverriders::getOverrider(const clang::CXXMethodDecl*, clang::CharUnits) const: Assertion `OverridersMap.count(std::make_pair(MD, BaseOffset)) && "Did not find overrider!"' failed.

llvm-svn: 230406