LibWeb: Don't send audio time updates until audio is playing

We would start the timer to send playback time updates to the element
before playback had started, so in cases where the `HTMLMediaElement`
(incorrectly) creates both an `AudioTrack` and `VideoTrack`, it will
not cause the seek bar to flicker between the current video position
and zero.

Userland/Libraries/LibWeb/Platform/AudioCodecPluginAgnostic.cpp

@@ -78,7 +78,6 @@ AudioCodecPluginAgnostic::AudioCodecPluginAgnostic(NonnullRefPtr<Audio::Loader>
     m_update_timer->on_timeout = [this]() {
         update_timestamp();
     };
-    m_update_timer->start();
 }
 
 void AudioCodecPluginAgnostic::resume_playback()