issue: #29677#29838
during get shard leaders, if qeurynode doesn't ack the heartbeat than
10s, querycoord will treat it as unavailable, and won't return shard
leader on it. but when querynode has a full cpu usage, it's easily to
stuck for more than 10s without ack the heartbeat, which cause no shard
leader to search/query.
This PR remove heartbeat lag logic during get shard leaders
Signed-off-by: Wei Liu <wei.liu@zilliz.com>