fix(collapse): remove element height watching

For unclear reasons the directive was watching DOM element's height
which incurs performance penalty. Normally this watching shouldn't be
necessery as collapsible elements should get height: auto;

Closes #1222

src/collapse/collapse.js

@@ -22,23 +22,7 @@ angular.module('ui.bootstrap.collapse',['ui.bootstrap.transition'])
 
       var isCollapsed;
       var initialAnimSkip = true;
-      scope.$watch(function (){ return element[0].scrollHeight; }, function (value) {
-        //The listener is called when scollHeight changes
-        //It actually does on 2 scenarios: 
-        // 1. Parent is set to display none
-        // 2. angular bindings inside are resolved
-        //When we have a change of scrollHeight we are setting again the correct height if the group is opened
-        if (element[0].scrollHeight !== 0) {
-          if (!isCollapsed) {
-            if (initialAnimSkip) {
-              fixUpHeight(scope, element, element[0].scrollHeight + 'px');
-            } else {
-              fixUpHeight(scope, element, 'auto');
-            }
-          }
-        }
-      });
-
+
       scope.$watch(attrs.collapse, function(value) {
         if (value) {
           collapse();

src/collapse/test/collapse.spec.js

@@ -86,21 +86,5 @@ describe('collapse directive', function () {
       expect(element.height()).toBeLessThan(collapseHeight);
     });
 
-    it('should shrink accordingly when content size inside collapse decreases on subsequent use', function() {
-      scope.isCollapsed = false;
-      scope.exp = false;
-      scope.$digest();
-      scope.isCollapsed = true;
-      scope.$digest();
-      scope.isCollapsed = false;
-      scope.$digest();
-      $timeout.flush();
-      scope.exp = true;
-      scope.$digest();
-      var collapseHeight = element.height();
-      scope.exp = false;
-      scope.$digest();
-      expect(element.height()).toBeLessThan(collapseHeight);
-    });
   });
 });