Make sure transition tile images are not embedded twice

[Geokureli]

In #396, images were embedded via include.xml, this may cause it to be embedded twice. This is not the end of the world, since the PR also reduces their size by more than half. Let's find out, for future reference and, if needed, see if we can prevent double embed in some way

[Geokureli]

Its embedded twice (for sure on html5)
https://community.openfl.org/t/double-embedding-images-with-bitmap-and-include-xml/13745/4