[1.x] Clean up route definition for Single Action Controllers

[istiak-tridip]

Laravel added support for Single Action/Invokable Controller since v5.6. According to the documentation:

When registering routes for single action controllers, you do not need to specify a controller method. Instead, you may simply pass the name of the controller to the router

This PR cleans up the route files by removing the unnecessarily specified __invoke method for the Single Action controllers.

These changes should not cause any breaking changes.