Remove incorrect comment in getSingleUndroppableUse. NFC

We traverse the entire use list to find the undroppable use.

Author: annamthomas

llvm/include/llvm/IR/Value.h

@@ -454,9 +454,6 @@ class Value {
 
   /// Return true if there is exactly one use of this value that cannot be
   /// dropped.
-  ///
-  /// This is specialized because it is a common request and does not require
-  /// traversing the whole use list.
   Use *getSingleUndroppableUse();
   const Use *getSingleUndroppableUse() const {
     return const_cast<Value *>(this)->getSingleUndroppableUse();