issue: #30816
cause balance channel will stuck until leader view catch up the current
target, then start to unsub the old delegator. which make sure that the
new delegator can provide search before release old delegator. but
another logic in segment_checker skip loading segment during balance
channel. so during balance channel, if query node crash, new delegator
can't catch up target forever, then stuck forever.
This PR remove the rule that skip loading segment during balance channel
to avoid the logic dead lock here.
Signed-off-by: Wei Liu <wei.liu@zilliz.com>