Fixed sound that could be heard from much too far away on certain maps.

[Vitroze]

On certain maps, the sound distance is far too great, meaning an approaching motorcycle can always be heard despite the already low volume. This PR fixes the issue.

Fix : #352

[StyledStrike]

Manually calculating the attenuation is not the correct way to deal with this, plus it can cause confusion in the code given that it is applied on top of what the PannerNode is already doing.

[StyledStrike]

As for setting onload/onerror/onabort to null when removing the layer, that should probably done before the request is aborted, which I've done on b313df7

[Vitroze]

Manually calculating the attenuation is not the correct way to deal with this, plus it can cause confusion in the code given that it is applied on top of what the PannerNode is already doing.

I'll look into integrating another solution instead of creating the "attenuation."