Fix crash with detach tab / hide tab buttons

Summary:
Lambdas don't auto disconnect. Removing that code also
removed one of Nathan's nitpicks on my code.

Reviewers: #konsole, hindenburg, sandsmark

Reviewed By: #konsole, hindenburg

Subscribers: konsole-devel

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D14298