log errors from removing unix domain paths?

[slingamn]

We got a bug report in #ergo like so:

1. Ergo was accidentally run as root
2. This created a root-owned unix domain socket path corresponding to one of the listeners
3. Starting Ergo again as the unprivileged role user, os.Remove failed silently:

   ergo/irc/listeners.go

   Line 50 in 1f4b524

   os.Remove(addr)

4. The server then failed to start with: Apr 03 13:02:20 hostname start.sh[1545]: 2024-04-03T13:02:20.983Z : error : server : Could not load server: listen unix /tmp/ergo_websocket: bind: address already in use
5. Head scratching ensued

We don't want to log the error unconditionally since the file not existing is not an error, but we could maybe do a better job here