chore(tabs): remove disabled support

- Remove deprecated `disabled` support

Closes #4383

Author: wesleycho

Diff for: src/tabs/tabs.js

@@ -186,7 +186,7 @@ angular.module('ui.bootstrap.tabs', [])
   </file>
 </example>
  */
-.directive('tab', ['$parse', '$log', function($parse, $log) {
+.directive('tab', ['$parse', function($parse) {
   return {
     require: '^tabset',
     restrict: 'EA',
@@ -217,17 +217,6 @@ angular.module('ui.bootstrap.tabs', [])
         });
       }
 
-      // Deprecation support of "disabled" parameter
-      // fix(tab): IE9 disabled attr renders grey text on enabled tab #2677
-      // This code is duplicated from the lines above to make it easy to remove once
-      // the feature has been completely deprecated
-      if (attrs.disabled) {
-        $log.warn('Use of "disabled" attribute has been deprecated, please use "disable"');
-        scope.$parent.$watch($parse(attrs.disabled), function(value) {
-          scope.disabled = !! value;
-        });
-      }
-
       scope.select = function() {
         if (!scope.disabled) {
           scope.active = true;