(but keep support for it for backward compatibility)
The only place where wsrep-lib made use of WSREP_KEY_SHARED is
wsrep::append_sr_keys_for_commit() which is used only with protocols >= 4
so we don't need to worry about the protocol version and just change
wsrep:๐:shared to wsrep:๐:reference.
Refs codership/wsrep-lib#227