drain_on_shutdown: Simplify
drain_on_shutdown: Simplify

The modern version of this method doesn't need the
run_with_no_api_lock(), as it's launched on shard 0
anyway, neither it needs logging before and after
as it's done by the deferred action from main that
calls it.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla