Fix various clear_map issues

After CleverRaven#30051 clear_creatures no longer clears NPCs.  Add a call to do
that in these tests where it is needed.

Also, in clear_map, remove NPCs before vehicles to avoid unboarding
errors (as already hinted at in npc_test.cpp).

Simplify npc_test to use the new improved clear_map.

Ultimately, this is all a workaround for the fact that vehicle detaching
does not properly mark NPCs as not in the vehicle.  That should also be
fixed.

tests/map_helpers.cpp

@@ -73,10 +73,13 @@ void clear_map()
     for( int z = -2; z <= 0; ++z ) {
         clear_fields( z );
     }
-    wipe_map_terrain();
-    g->m.clear_traps();
+    // Remove NPCs before vehicles otherwise you get unboarding errors
+    // TODO: Fixc vehicle detaching so that it removes boarded NPCs first, so
+    // that this is not a problem.
     clear_npcs();
     clear_creatures();
+    wipe_map_terrain();
+    g->m.clear_traps();
 }
 
 void clear_map_and_put_player_underground()

tests/monster_test.cpp

@@ -26,7 +26,7 @@ typedef statistics<int> move_statistics;
 static int moves_to_destination( const std::string &monster_type,
                                  const tripoint &start, const tripoint &end )
 {
-    clear_creatures();
+    clear_map();
     REQUIRE( g->num_creatures() == 1 ); // the player
     monster &test_monster = spawn_test_monster( monster_type, start );
     // Get it riled up and give it a goal.
@@ -83,7 +83,7 @@ std::ostream &operator << ( std::ostream &os, const std::vector<track> &vec )
  **/
 static int can_catch_player( const std::string &monster_type, const tripoint &direction_of_flight )
 {
-    clear_creatures();
+    clear_map();
     REQUIRE( g->num_creatures() == 1 ); // the player
     player &test_player = g->u;
     // Strip off any potentially encumbering clothing.

tests/npc_test.cpp

@@ -316,14 +316,8 @@ TEST_CASE( "npc-movement" )
 
     g->place_player( tripoint( 60, 60, 0 ) );
 
-    // kill npcs before removing vehicles so they are correctly unboarded
-    clear_npcs();
-    clear_creatures();
-    // remove existing vehicles
-    VehicleList vehs = g->m.get_vehicles( g->u.pos(), g->u.pos() + point( width - 1, height - 1 ) );
-    for( auto &veh : vehs ) {
-        g->m.detach_vehicle( veh.v );
-    }
+    clear_map();
+
     for( int y = 0; y < height; ++y ) {
         for( int x = 0; x < width; ++x ) {
             const char type = setup[y][x];