Make sure ref field in manual trigger dialog is cleared

static/js/directives/ui/manual-trigger-build-dialog.js

@@ -57,6 +57,8 @@ angular.module('quay').directive('manualTriggerBuildDialog', function () {
               $scope.fieldOptions[parameter['name']] = resp['values'];
             });
           }
+
+          delete $scope.parameters[parameter['name']];
         }
 
         $scope.runParameters = parameters;