In editor - removing the last node of a midi cc in a lane - does not remove it completely.
A line remains - and this only value will always be sent.
It seems that code running this is the same as for all automation editing, as well a tempo track that works like this - you can remove all nodes, but a horisontal line remains..
But for midi - you should be able to remove all of a certain midi cc - when last node is removed.
It's not like built in automation or tempo map.
Workaround now is to move to another daw like Sonar or Cubase for this, then import that midi again.
Or select all notes and other midi cc that is to remain - and copy to a new track, and discard the clip with non-grata midi cc.
This is both very cumbersome.