[ADT] Delete orphaned doxygen comment in PriorityWorklist

[rdwampler]

Summary

The comment was added in r290952, but I believe the corresponding function was accidentally lost since the fix in r290954 seems related. So a more appropriate diff would add it back, but I am not familiar at all with the code to attempt that. I only noticed this while casually browsing the source code and wasn't sure how else to bring this to your attention so I thought I would submit this diff.

[rdwampler]

ping?

include/llvm/ADT/PriorityWorklist.h

if (E == V.end())
       return false;
     for (auto I = V.begin(); I != E; ++I)
       if (*I != T())
         M[*I] = I - V.begin();
     V.erase(E, V.end());
     return true;
   }
 
-  /// Reverse the items in the PriorityWorklist.
-  ///
-  /// This does an in-place reversal. Other kinds of reverse aren't easy to
-  /// support in the face of the worklist semantics.
-
   /// Completely clear the PriorityWorklist
   void clear() {
     M.clear();
     V.clear();
   }
 
 private:
   /// A wrapper predicate designed for use with std::remove_if.