fix(tooltip): remove extra digest causing incompatibility

In Angular 1.3.1, when using tooltips with ngAnimate, this extra $digest
call seems to break ngClass. This is an extra call to ngAnimate and it
shouldn’t be called since the tooltip hasn’t been added to the DOM.

I was unable to create a test case to test compatibility with ngAnimate.

Fixes #2951
Fixes #2959

src/tooltip/tooltip.js

@@ -237,7 +237,6 @@ angular.module( 'ui.bootstrap.tooltip', [ 'ui.bootstrap.position', 'ui.bootstrap
               }
               tooltipLinkedScope = ttScope.$new();
               tooltip = tooltipLinker(tooltipLinkedScope, angular.noop);
-              ttScope.$digest();
             }
 
             function removeTooltip() {