[C++11] Add 'override' keyword to virtual methods that override their base class.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@203893 91177308-0d34-0410-b5e6-96231b3b80d8
Remove seemingly dead method. It was marked virtual but doesn't override anything and there don't seem to be any in tree callers.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@203894 91177308-0d34-0410-b5e6-96231b3b80d8
De-virtualize a method that doesn't override anything and has no overrides itself.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@203895 91177308-0d34-0410-b5e6-96231b3b80d8