Remove the -fuse-gold-plugin driver option.

* It was redundant with -flto.
* It was confusing since -uAnythingElse is a different option.
* GCC uses -fuse-linker-plugin, so it was not even a compatibility option.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@189976 91177308-0d34-0410-b5e6-96231b3b80d8