placement: remove isolationlevel (#30859)

close #30858

ddl/placement/bundle_test.go

@@ -352,7 +352,7 @@ func (s *testBundleSuite) TestString(c *C) {
 	c.Assert(err, IsNil)
 	bundle.Rules = append(rules1, rules2...)
 
-	c.Assert(bundle.String(), Equals, `{"group_id":"TiDB_DDL_1","group_index":0,"group_override":false,"rules":[{"group_id":"","id":"","start_key":"","end_key":"","role":"voter","count":3,"label_constraints":[{"key":"zone","op":"in","values":["sh"]}],"location_labels":["region","zone","rack","host"],"isolation_level":"region"},{"group_id":"","id":"","start_key":"","end_key":"","role":"voter","count":4,"label_constraints":[{"key":"zone","op":"notIn","values":["sh"]},{"key":"zone","op":"in","values":["bj"]}],"location_labels":["region","zone","rack","host"],"isolation_level":"region"}]}`)
+	c.Assert(bundle.String(), Equals, `{"group_id":"TiDB_DDL_1","group_index":0,"group_override":false,"rules":[{"group_id":"","id":"","start_key":"","end_key":"","role":"voter","count":3,"label_constraints":[{"key":"zone","op":"in","values":["sh"]}],"location_labels":["region","zone","rack","host"]},{"group_id":"","id":"","start_key":"","end_key":"","role":"voter","count":4,"label_constraints":[{"key":"zone","op":"notIn","values":["sh"]},{"key":"zone","op":"in","values":["bj"]}],"location_labels":["region","zone","rack","host"]}]}`)
 
 	c.Assert(failpoint.Enable("github.com/pingcap/tidb/ddl/placement/MockMarshalFailure", `return(true)`), IsNil)
 	defer func() {

ddl/placement/rule.go

@@ -58,7 +58,6 @@ func NewRule(role PeerRoleType, replicas uint64, cnst Constraints) *Rule {
 		Count:          int(replicas),
 		Constraints:    cnst,
 		LocationLabels: []string{"region", "zone", "rack", "host"},
-		IsolationLevel: "region",
 	}
 }