mail/mboxgrep: update to 0.7.10

• switch to upstream's new hoster
• remove lots of old hacks and patches
• remove hacked in OpenSSL dependency
• patch makefiles to enable staging
• adopt this unmaintained port

Changelog: https://git.datatipp.se/dspiljar/mboxgrep/releases/tag/0.7.10

Approved by: flo (mentor)
Differential Revision: https://reviews.freebsd.org/D38782