chore: update readme

packages/runtime-core/README.md

@@ -7,7 +7,7 @@ For full exposed APIs, see `src/index.ts`. You can also run `yarn build runtime-
 ## Building a Custom Renderer
 
 ``` ts
-import { createRenderer, createAppAPI } from '@vue/runtime-core'
+import { createRenderer } from '@vue/runtime-core'
 
 const { render, createApp } = createRenderer({
   patchProp,