chore(runtime-vapor): remove simpleSetCurrentInstance export

Author: johnsoncodehk

packages/runtime-vapor/src/index.ts

@@ -42,9 +42,3 @@ export {
   applyDynamicModel,
 } from './directives/vModel'
 export { withVaporDirectives } from './directives/custom'
-
-/**
- * TODO: Somehow remove this line which causes performance regression on select key.
- * @internal
- */
-export { simpleSetCurrentInstance } from '@vue/runtime-core'