[prefer-spy-on] duplicate `mockImplementation` in autofix

Given the following code:

```ts
foo.bar = jest.fn().mockImplementation(baz => baz)
```

The `jest/prefer-spy-on` rule autofixes this to:

```ts
jest.spyOn(foo, 'bar').mockImplementation().mockImplementation(baz => baz)
```

The `mockImplementation` should rather be deduplicated. Expected autofix:

```ts
jest.spyOn(foo, 'bar').mockImplementation(baz => baz)
```