High: executor: fix regression in remote node shutdown

This reverts the essential part of d61494347, which was based on misdiagnosing
a remote node shutdown issue. Initially, it was thought that a "TLS server
session ended" log just after a remote node requested shutdown indicated that
the proxy connection coincidentally dropped at that moment. It actually is the
routine stopping of accepting new proxy connections, and existing when that
happens makes the remote node exit immediately without waiting for the
all-clear from the cluster.

Fixes T361