switch to official extend selection API

editors/code/src/commands/index.ts

@@ -1,6 +1,5 @@
 import * as analyzerStatus from './analyzer_status';
 import * as applySourceChange from './apply_source_change';
-import * as extendSelection from './extend_selection';
 import * as joinLines from './join_lines';
 import * as matchingBrace from './matching_brace';
 import * as onEnter from './on_enter';
@@ -11,7 +10,6 @@ import * as syntaxTree from './syntaxTree';
 export {
     analyzerStatus,
     applySourceChange,
-    extendSelection,
     joinLines,
     matchingBrace,
     parentModule,