End-of-life (EOL) of FlexRAN

FlexRAN has been OpenAirInterface's (4G) RAN Controller before there was
O-RAN or an E2 interface. It has been initially merged with tag
2016.w49. Multiple iterations added functionality to control the MAC; to
dynamically add multiple MMEs; to control handover; to retrieve
statistics of MAC, RLC, PDCP, GTP, RRC, S1AP; to control slicing
operation; and other functionality, to name a few.

Development has stalled, and another controller named FlexRIC, based on
the E2 interface, has been implemented. The latter's E2 Agent will be
added to OAI soon. The now deprecated FlexRAN is therefore removed in
preparation to merge FlexRIC's E2 Agent in the future.
This tag has no release notes.