fix(tooltip): race condition when setting position

A race condition could occur when there is an open delay that
doesn't get cancelled after the transition delay resulting in
the position logic getting called.  This will then try to set
the css of the tooltip after is has been destroyed in the
removeTooltip function.

Closes #4765
Fixes #4757

src/tooltip/tooltip.js

@@ -252,9 +252,6 @@ angular.module('ui.bootstrap.tooltip', ['ui.bootstrap.position', 'ui.bootstrap.s
 
             // Hide the tooltip popup element.
             function hide() {
-              cancelShow();
-              cancelHide();
-
               if (!ttScope) {
                 return;
               }
@@ -307,9 +304,10 @@ angular.module('ui.bootstrap.tooltip', ['ui.bootstrap.position', 'ui.bootstrap.s
             }
 
             function removeTooltip() {
+              cancelShow();
+              cancelHide();
               unregisterObservers();
 
-              transitionTimeout = null;
               if (tooltip) {
                 tooltip.remove();
                 tooltip = null;
@@ -501,8 +499,6 @@ angular.module('ui.bootstrap.tooltip', ['ui.bootstrap.position', 'ui.bootstrap.s
 
             // Make sure tooltip is destroyed and removed.
             scope.$on('$destroy', function onDestroyTooltip() {
-              cancelShow();
-              cancelHide();
               unregisterTriggers();
               removeTooltip();
               openedTooltips.remove(ttScope);