Remove doc of a missing feature of the tilemap select tool

Right clicking with the tilemap select tool doesn't remove the
selection so remove the documentation about it.
Document the behavior of the Delete key.

tutorials/2d/using_tilemaps.rst

@@ -202,9 +202,7 @@ To remove from the current selection, hold :kbd:`Ctrl` then select a tile.
 The selection can then be used in any other painting mode to quickly create copies
 of an already-placed pattern.
 
-While in Selection mode, you can't place new tiles, but you can still erase
-tiles by right-clicking after making a selection. The whole selection will be erased,
-regardless of where you click in the selection.
+You can remove the selected tiles from the TileMap by pressing :kbd:`Del`.
 
 You can toggle this mode temporarily while in Paint mode by holding :kbd:`Ctrl`
 then performing a selection.