[skip ci] Add comment for freeAll (#11591)

Signed-off-by: bigsheeper <yihao.dai@zilliz.com>

internal/querynode/collection_replica.go

@@ -118,6 +118,7 @@ type ReplicaInterface interface {
 
 	// getSegmentsMemSize get the memory size in bytes of all the Segments
 	getSegmentsMemSize() int64
+	// freeAll will free all meta info from collectionReplica
 	freeAll()
 	printReplica()
 }