Cleanup KIO servicemenu for sign / encrypt files

These actions provide the "sign" and "encrypt" actions e.g., in dolphin's context menu.
There were previously separate actions for encrypting, pgp-signing and smime-signing, which all lead
to the exact same dialog which then allows arbitrary operations, even those different from what the action said.
Since we don't have these split-up actions in other places (and are removing them where we do have them), let's
remove them here as well. A unified "Sign/Encrypt" action already existed, the name has just been changed slightly to
be the same as we use elsewhere