community/tinyssh: remove dependency to ucspi-tcp6

ucspi-tcp6 is an obsolete package that conflicts with abuild. In order for tinysshd to keep working, we make it use s6-networking's s6-tcpserver instead of ucspi-tcp6's tcpserver. This adds a few dependencies, because s6-networking actually uses dynamic libraries whereas ucspi-tcp6 bundles everything in.

This commit also removes the use of supervise-daemon, which mangles server command lines and does not bring any real supervision value.