Lua AIs: use ai_helper.robust_move_and_attack()

ai_helper.robust_move_and_attack() does the stop_unit_moves automatically if the unit is at the destination hex.

(cherry-picked from commit fdc3249496)

data/ai/micro_ais/cas/ca_herding_herd_sheep.lua

@@ -73,11 +73,7 @@ function ca_herding_herd_sheep:execution(cfg)
          end
     end
 
-    if (best_hex[1] == best_dog.x) and (best_hex[2] == best_dog.y) then
-        AH.checked_stopunit_moves(ai, best_dog)
-    else
-        AH.checked_move(ai, best_dog, best_hex[1], best_hex[2])  -- partial move only!
-    end
+    AH.robust_move_and_attack(ai, best_dog, best_hex, nil, { partial_move = true })
 end
 
 return ca_herding_herd_sheep

data/campaigns/Two_Brothers/ai/ca_muff_toras_move.lua

@@ -64,8 +64,6 @@ function muff_toras_move:execution()
 
     if ((go_to[1] ~= muff_toras.x) or (go_to[2] ~= muff_toras.y)) then
         AH.robust_move_and_attack(ai, muff_toras, go_to)
-    else
-        AH.checked_stopunit_moves(ai, muff_toras)
     end
 
     -- Test whether an attack without retaliation or with little damage is possible