Fix comment, per bug 520661 comment 4.

xpcom/glue/nsDeque.cpp

@@ -169,10 +169,7 @@ nsDeque& nsDeque::Erase() {
  * If the deque actually overflows, there's very little we can do.
  * Perhaps this function should return PRBool/nsresult indicating success/failure.
  *
- * @return  capacity of the deque
- *          If the deque did not grow,
- *          and you knew its capacity beforehand,
- *          then this would be a way to indicate the failure.
+ * @return  whether growing succeeded
  */
 PRBool nsDeque::GrowCapacity() {
   PRInt32 theNewSize=mCapacity<<2;