Remove redundant checks in HandleObstructedMove performed already by PathResult

HandleObstructedMove contains logic to drop long waypoints, should they be occupied by units (because that can get the pathfinder stuck, since the long-range pathfinder can find a path, but not the vertex one).

However PathResult already drops waypoints this way, so this code can be removed for simplification.

Differential Revision: https://code.wildfiregames.com/D1981