Dynamic TileMap layer demo is obsolete

[KoBeWi]

Which demo project is affected:
Dynamic TileMap layers

Description:
The dynamic TileMap layers demo added in #954 is pretty much obsolete now. The point was to show how to disable collisions for a layer dynamically, but with the new TileMapLayer it's a simple checkbox in the inspector, so all the dynamic magic is unnecessary.

Runtime modifications allow for some advanced editing of TileMapData, but personally I don't use it anymore and can't think of a practical use. Either the demo needs a new use-case or it should be deprecated (if that's a thing here).