This class is being used when $this->broker->reset() is called: https://github.com/laravel/framework/blob/56a58e0fa3d845bb992d7c64ac9bb6d0c24b745a/src/Illuminate/Auth/Passwords/PasswordBroker.php
And inside that password broker the credentials are checked. Because you removed the email address the logic inside that class is 'broken' and will never give green lights for the password reset.
You need to create your own password broker and overwrite it. I never had to do that so I can't give you any tips on that. But with the proper search keywords you should be able to figure that out with Google.
- https://stackoverflow.com/questions/40532296/laravel-5-3-password-broker-customization
- https://laracasts.com/discuss/channels/general-discussion/laravel-5-password-broker?page=1
But before you start all this customization ask yourself if you really need to change the default behavior of Laravel. It ain't a problem to do it but if you start changing default behavior you also need to maintain it during upgrades to newer versions.