Remote Assistance.app: Privately bundle ssvnc

[probonopd]

ssvnc was removed from FreeBSD ports and packages because it gets no further updates upstream:

https://www.freshports.org/commit.php?message_id=97cf09b1df1318292899840cfc300d5072a1d670

We either need to find a replacement or need to privately bundle it. Extra work.

[probonopd]

net/ssvnc: Deprecate and set expiration date to 2022-03-31

Abandonware, last release in 2011 and broken functionality
reported upstream

Looks like we need to scan for such messages somehow. Can it be automated?

Also, having just one quarter "early warning" is not sufficient!