Remove socketee support

[Firefishy]

Why remove socketee support?

• The upstream https://github.com/discourse/socketee/ project has been archived.
• socketee is not built for ARM64 and it breaks building / running this image on ARM64.

[Firefishy]

I would be happy to create another PR to add building arm64 image support if this PR is merged.

[Firefishy]

If SOCKETEE_RELAY_SOCKET is used by Civilized Discourse Construction Kit I'd be happy to re-do this PR by removing socketee and instead use socat directly

eg:

socat -u -b 8192 -v \
  UNIX-RECV:/dev/log,unlink-early,mode=0666 \
  UNIX-SENDTO:"$SOCKETEE_RELAY_SOCKET"

[Firefishy]

@cvx Maybe you could look at this?