encoder: remove the "bitDepth" getter/setter
encoder: remove the "bitDepth" getter/setter

Now that formats other than int 16-bit are supported, this serves no purpose

TooTallNate/node-lame,dag10/node-lame,TooTallNate/node-lame,TooTallNate/node-lame,mcanthony/node-lame,EQ4/node-lame,mcanthony/node-lame,PlayNetwork/node-lame,PlayNetwork/node-lame,PlayNetwork/node-lame,mcanthony/node-lame,dag10/node-lame,EQ4/node-lame,dag10/node-lame,EQ4/node-lame