remove unused import value from doc

Author: Alphonso Tran

docs/api/createAsyncThunk.mdx

@@ -521,7 +521,7 @@ If a thunk was cancelled, the result of the promise will be a `rejected` action
 So if you wanted to test that a thunk was cancelled before executing, you can do the following:
 
 ```ts no-transpile
-import { createAsyncThunk, isRejected } from '@reduxjs/toolkit'
+import { createAsyncThunk } from '@reduxjs/toolkit'
 
 test('this thunk should always be skipped', async () => {
   const thunk = createAsyncThunk(