Deleting a movement order instead duplicates it

**Describe the bug**
Deleting a movement order from a fleet causes it to be duplicated at the end of the queue instead.

**Steps to reproduce**
1. Select a fleet (not sure if this works with individual ships).
2. Give it some orders.
3. Delete one of the orders (from the fleet's orders tab).

**Expected behavior**
The order is deleted.

**Actual behavior**
The order is copied to the end of the queue.

**Screenshots**
N/A

**Related issues**
N/A

**Testing plan**
???

**Additional context**
N/A