fix(typeahead): remove duplicate id attribute

* remove any duplicate `id` attribute on the typeahead hint element if used on
  the original input element.

BREAKING CHANGE: This change removes the `id` attribute on the first `<input>`
element placed into the DOM when the `typeahead-show-hint` attribute is used
and there is an `id` attribute present on the original `uib-typeahead` element.
This could affect selectors if they are being used.

Fixes angular-ui#5926

src/typeahead/test/typeahead.spec.js

@@ -222,8 +222,6 @@ describe('typeahead tests', function() {
         expect(element).toBeClosed();
     });
 
-
-
     it('should support custom model selecting function', function() {
       $scope.updaterFn = function(selectedItem) {
         return 'prefix' + selectedItem;
@@ -470,6 +468,15 @@ describe('typeahead tests', function() {
       };
       expect(prepareInvalidDir).toThrow();
     });
+
+    it('should remove the id attribute from the original DOM element', function() {
+      var element = prepareInputEl('<div><input id="typeahead-element" ng-model="result" uib-typeahead="item for item in source | filter:$viewValue" typeahead-show-hint="true"></div>');
+      var inputEl = findInput(element);
+
+      expect(inputEl.size()).toBe(2);
+      expect(inputEl.eq(0).attr('id')).toBe(undefined);
+      expect(inputEl.eq(1).attr('id')).toBe('typeahead-element');
+    });
   });
 
   describe('shouldSelect', function() {

src/typeahead/typeahead.js

@@ -152,6 +152,10 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.debounce', 'ui.bootstrap
         'vertical-align': 'top',
         'background-color': 'transparent'
       });
+
+      if (hintInputElem.attr('id')) {
+        hintInputElem.removeAttr('id'); // remove duplicate id if present.
+      }
       inputsContainer.append(hintInputElem);
       hintInputElem.after(element);
     }