Remove useless ivar assign in controller spec

This assignment is not necessary here.

Author: riseshia

lib/generators/rspec/scaffold/templates/controller_spec.rb

@@ -45,7 +45,7 @@
 <% unless options[:singleton] -%>
   describe "GET #index" do
     it "returns a success response" do
-      <%= file_name %> = <%= class_name %>.create! valid_attributes
+      <%= class_name %>.create! valid_attributes
 <% if Rails::VERSION::STRING < '5.0' -%>
       get :index, {}, valid_session
 <% else -%>