mail/alpine: Update to 2.21.1

• Move to new master site. The old one is gone.
• The maildir patch is gone too, so remove the MAILDIR option for now.
• While here add LICENSE_FILE and fix plist

PR: 226790
Submitted by: Alexandre C. Guimarães <lebarondemerde@privacychain.ch>
Approved by: Marco Beishuizen <mbeis@xs4all.nl> (maintainer)