In the past the discovery configuration expected, that we can support multiple
API server endpoints. In practice, we always end up with a single API server
endpoint, because, even in HA setups, we use a load balancer scheme for API
servers.
Therefore, to reduce complexity and improve readability of the config, the
multiple API server endpoints support is removed from the bootstrap token
discovery join method and configuration.
Signed-off-by: Rostislav M. Georgiev <rostislavg@vmware.com>