remove probes of the lighthouse(s)

[rawdigits]

Probing a LH isn't actually very useful, since recv_error should catch issues. this avoids stampeding a LH by dropping good tunnels during a reconnect spike.

I debated putting this in connection_manager.go under the Out method, but checking there would mean putting IsLighthouseIP, which has a lock, into the hot path. Instead, allow these IPs to go into the wheel, but just delete them instead of probing.

We may want to make this behavior optional via config, but I'm inclined to say this is more correct than we we do now, and the old behavior is of dubious value.