Revert "[LTO/gold] Support --wrap"

This reverts commit r327459. The new gold plugin interface is not
available with older gold installations, leading to compile failures:
http://lab.llvm.org:8011/builders/clang-with-thin-lto-ubuntu/builds/9109/steps/build-stage2-LLVMgold.so/logs/stdio

llvm-svn: 327465