SoundManagerIOS: Remove unsupported/redundant options

[fwcd]

On iPadOS using AVAudioSessionCategoryOptionAllowAirPlay seems to throw an AVAudioSessionErrorCodeBadParam and according to the docs it only seems to be allowed when the category is set to AVAudioSessionCategoryPlayAndRecord (which we don't). This PR therefore removes it.

The option AVAudioSessionCategoryOptionAllowBluetoothA2DP seems to be redundant too, this seems to already be covered by AVAudioSessionCategoryPlayback (the category that we use for now), therefore we remove it too.

In the future we may wish to investigate using AVAudioSessionCategoryMultiRoute for more fine-grained control over audio routing, but this also seems to disable the device's volume buttons, so we should look into this more deeply before using this configuration.

[m0dB]

Reading the apple docs, I agree with your assessment.