events: improve removeListener() performance

array.shift() seems to be faster than arrayClone() when the item
to remove is at the front (at least with V8 5.4).

PR-URL: https://github.com/nodejs/node/pull/10572
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

lib/events.js

@@ -360,6 +360,8 @@ EventEmitter.prototype.removeListener =
           } else {
             delete events[type];
           }
+        } else if (position === 0) {
+          list.shift();
         } else {
           spliceOne(list, position);
         }