Revert r141657 for now. This has broken css and changed links on llvm…

….org. I'd like to understand exactly why the links have changed and if a newer doxygen is required. This may be reapplied once we upgrade on llvm.org and it is fully tested.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142686 91177308-0d34-0410-b5e6-96231b3b80d8