Remove attachmentservicemenu in favor of Purpose plugin
Summary: Since 5.48 Purpose has a FileItemActionPlugin that adds a "Send via Mail" action to Dolphin et al. It offers all the functionality of the KMail implementation, but respects the users prefered Email program. KDE Connect and BlueDevil dropped their custom actions in favor of Purpose plugins, too.
Test Plan: "Send as Email Attachment" action no longer appears in Dolphin. Can still send emails via "Share->Send via Email"
Reviewers: KDE PIM: KMail, mlaurent
Reviewed By: mlaurent
Subscribers: kde-pim
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D14811