[skip ci]Add comment for NewDeregisterPolicy (#10133)

Signed-off-by: Nsunby <bingyi.sun@zilliz.com>

internal/datacoord/channel_manager_factory.go

@@ -82,6 +82,7 @@ func (f *ConsistentHashChannelPolicyFactory) NewRegisterPolicy() RegisterPolicy
 	return ConsistentHashRegisterPolicy(f.hashring)
 }
 
+// NewDeregisterPolicy create a new dereigster policy
 func (f *ConsistentHashChannelPolicyFactory) NewDeregisterPolicy() DeregisterPolicy {
 	return ConsistentHashDeregisterPolicy(f.hashring)
 }