If a relay has no family we should omit it or put the relay's fingerprint in it

Currently, if a relay has no family declared we get something like:

[+] Nickname: hhrtQKEYrhnSTpg3QNJ
  > Fingerprint: Rsa: $0262871FEE026971C86BD7264D6D0482CEE29671, Ed: UaK9ZRTwYyo7cEo5yJGjrex12+Ne8NRQe5GGnjN5/9g
  > Flags: RelayFlags(RUNNING | VALID | V2DIR)
  > Weight: Unmeasured(20)
  > Version: 0.4.7.14
  > ORPort(s): 208.115.225.74:443
  > IPv4 Policy: reject 1-65535
  > IPv6 Policy: reject 1-65535
  > Family: 

when doing the margot find command. Family: is not super informative. Instead we could just omit the family entry altogether if there is no family configured. That would save space while conveying the same info. Less preferred we could put the relay's fingerprint in that field instead.