Fix #9869: remove docking tile when doing a clear square

Terraforming through objects placed on water didn't properly remove docking tiles as expected.

By moving some logic regarding removal of docking tiles into DoClearSquare, the issue is solved, while also simplifying code, avoiding repetition elsewhere.

src/rail_cmd.cpp

@@ -1819,9 +1819,7 @@ static CommandCost ClearTile_Track(TileIndex tile, DoCommandFlag flags)
 
 				/* The track was removed, and left a coast tile. Now also clear the water. */
 				if (flags & DC_EXEC) {
-					bool remove = IsDockingTile(tile);
 					DoClearSquare(tile);
-					if (remove) RemoveDockingTile(tile);
 				}
 				cost.AddCost(_price[PR_CLEAR_WATER]);
 			}