Remove code related to Beats Central Management

[jen-huang]

BCM was removed in 7.14 (elastic/beats#25696, elastic/kibana#99789). There are still leftover references in ES code related to accessing .management-beats index and licensing that should be cleaned up.

Please see #30520, the original PR that introduced BCM-related code, for what to remove.

[elasticmachine]

Pinging @elastic/es-security (Team:Security)