This command is used to remove a viewport from a moan channel, previously added with Add Viewport To Channel.
If channelId is not specified, the viewport is removed from all the moan channels it is on.
When a viewport closed, it is automatically removed from all moan channels.
canvasId is the canvas that the viewport to be removed from the moan channel is viewing.
channelId is the optional moan channel to remove the viewport from.
See also Remove Sprite From Channel, Add Sprite To Channel and Add Viewport To Channel.