[golang] Move code out into a separate repo

[dkropachev]

Move code from https://github.com/scylladb/alternator-load-balancing/tree/master/go to https://github.com/scylladb/alternator-client-golang

Migrated to Jira: DRIVER-280

[dkropachev]

It has been moved to https://github.com/scylladb/alternator-client-golang