Remove unnecessary refcount increase when using m_player in MediaPlayerPrivateRemote

[Jean-Yves Avenard [:jya]]

As mentioned in: https://bugs.webkit.org/show_bug.cgi?id=232124#c3

We have a lot of this code pattern:
```
    if (RefPtr player = m_player.get())
        m_player->addAudioTrack(addResult.iterator->value);
```

there's no side effect possible when calling m_player here, so there's no need to keep a strong reference :

doing:
```
    if (m_player)
        m_player->addAudioTrack(addResult.iterator->value);
```

is fine

[Radar WebKit Bug Importer]

<rdar://problem/84574114>

[Jean-Yves Avenard [:jya]]

Created attachment 442336 [details]
Patch