remove unused code

Author: River2000i

tests/realtikvtest/ddltest/main_test.go

@@ -15,18 +15,13 @@
 package ddltest
 
 import (
-	"flag"
 	"testing"
 
 	"github.com/pingcap/tidb/pkg/config"
 	"github.com/pingcap/tidb/tests/realtikvtest"
 	"github.com/pingcap/tidb/tests/realtikvtest/testutils"
 )
 
-// FullMode is a flag identify it should be run in full mode.
-// In full mode, the test will run all the cases.
-var FullMode = flag.Bool("full-mode", false, "whether tests run in full mode")
-
 func TestMain(m *testing.M) {
 	config.UpdateGlobal(func(conf *config.Config) {
 		conf.Store = config.StoreTypeTiKV