Revert "Abort long-running unauthenticated SSH connections"

This reverts commit 3a2c8f2c.

The commit has been introduced in !582 (merged)

When gitlab-sshd has been released on production, the following errors appeared in the logs:

I haven't managed to reproduce/debug locally, but this kind of error happens when a connection is closed before Gitaly has sent all the data.

Timers in Go are infamous for being hard to set up: https://github.com/golang/go/issues/14383, so let's try and remove this functionality and see whether it helps. Then we can try to add it back carefully.