audio/jack: Update to 1.9.20 release.

The FreeBSD specific changes have been upstreamed, we can fetch the original
sources again. Development of the client examples and tools has been split
from the JACK server, move them to the new port jack-example-tools.

This also includes a fix for missing library symbols, see bug #257696.

Take maintainership of audio/jack and audio/jack-example-tools .

PR: 257696
PR: 261256

Submitted by:   Florian Walpen <dev@submerge.ch>
Approved by:	pi (implicit)