Revert "Maneuvers: merged definitions from LSTS/dune@75b975d1e6c5700fb6abb78a1a67bbcb8a8b5339"

This reverts commit 52d0d4951e43322e9b6acf960641071d4a41f417.
The messages on imc/master were actually more recent than those on dune/master.
Removed message AbortAcked.

Conflicts:
	IMC.xml