BridgeDB writes `keyid=` before fingerprints

While testing for #9499 (moved), I realised that if I request https://127.0.0.1:6789/bridges?transport=obfs3 (localhost because it's a local test instance) then BridgeDB hands back bridge lines like this:

obfs3 245.102.100.252:23619 keyid=59ca743e89b508e16b8c7c6d2290efdfd14eea98 

which is wrong and will need to be fixed before we hand out fingerprints. This should be easy, just figure out where this string is getting added and kill it with fire.