Remove option to send e-mail after approval

[arnowelzel]

Also see https://wordpress.org/support/topic/plugin-not-sending-e-mail-since-about-one-week/

With https://github.com/arnowelzel/worpdress-comment-reply-email-notification/commit/ea11f13572b4c5ad0ca47a9fdd65cd8007af8f55 a new option was introduced to disable sending e-mail on comment approval.

However this makes no sense - if comment a approval is not needed, e-mails will always be send. And if approval is needed, it makes no sense to disable sending e-mails.

Also there is no real usecase for the original filter cren_disable_email_notification_on_comment_approval.