refactor($compile): remove unnecessary assignment

Closes #15337

src/ng/compile.js

@@ -2386,7 +2386,6 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
         }
 
         if (!directive.templateUrl && directive.controller) {
-          directiveValue = directive.controller;
           controllerDirectives = controllerDirectives || createMap();
           assertNoDuplicate('\'' + directiveName + '\' controller',
               controllerDirectives[directiveName], directive, $compileNode);