[skip ci] Add comment for Delete (#11844)

Signed-off-by: Ndragondriver <jiquan.long@zilliz.com>

internal/proxy/impl.go

@@ -1382,6 +1382,7 @@ func (node *Proxy) Insert(ctx context.Context, request *milvuspb.InsertRequest)
 	return it.result, nil
 }
 
+// Delete delete records from collection, then these records cannot be searched.
 func (node *Proxy) Delete(ctx context.Context, request *milvuspb.DeleteRequest) (*milvuspb.MutationResult, error) {
 	sp, ctx := trace.StartSpanFromContextWithOperationName(ctx, "Proxy-Delete")
 	defer sp.Finish()