scanner: provide device name

[holiman]

This PR uses the http interface at 8008:setup/eureka_info to pick out the device name, if a device has been found via scanning.

$ go run .  scan --cidr 192.168.50.0/24 
Scanning...  scanned 0, current 192.168.50.0
  - 'Office speaker' at 192.168.50.88:8009
Scanned 256 uris in 1.609840334s

Also removes some leftovers from a previous PR.

[vishen]

Thanks for this @holiman!