refactor($compile): check removeWatches before calling

Previously we assigned `noop` if there was no function but there is no
performance advantage in doing this since the check would have to happen
either at assignment time or at call time.

Removing this use of `noop` makes the code clearer, IMO :-)

Closes angular#12528

Author: petebacondarwin

src/ng/compile.js

@@ -2073,7 +2073,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
               controllerForBindings = controller;
               removeControllerBindingWatches =
                   initializeDirectiveBindings(scope, attrs, controller.instance,
-                                              bindings, scopeDirective) || noop;
+                                              bindings, scopeDirective);
             }
           }
           for (i in elementControllers) {
@@ -2087,7 +2087,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
               $element.data('$' + i + 'Controller', controllerResult);
               if (controller === controllerForBindings) {
                 // Remove and re-install bindToController bindings
-                removeControllerBindingWatches();
+                removeControllerBindingWatches && removeControllerBindingWatches();
                 removeControllerBindingWatches =
                   initializeDirectiveBindings(scope, attrs, controllerResult, bindings, scopeDirective);
               }