Remove an event from a line's event layer by channel and index.
The RPE chart (modified in place).
Index of the target line.
Event layer index.
Which channel: 'moveX', 'moveY', 'rotate', 'alpha', or 'speed'.
'moveX'
'moveY'
'rotate'
'alpha'
'speed'
Index of the event to remove.
The removed event, or undefined if index is out of range.
undefined
Remove an event from a line's event layer by channel and index.