Fix a memory leak when remote address was allocated
in etet_pool (eternal memory pool) in recovery_follow_remote
(start of replication).

Remove fiber->data, as redundant and confusing.
fiber->f_data is sufficient for all possible needs.

Fix a bug when fiber_server::data was never initialized
but passed to "on_bind" callback of fiber_server
(this worked since no single "on_bind" callback uses
its "data" argument).