Worlds will not delete

The bug

When trying to delete a world, the world would still show up in the single player world selection screen. I was expecting the world to delete, but instead it just stayed in the world selection screen. To trigger this, create a world, (I just did creative, I don't know about survival) and attempt to delete it.

Code analysis / reason

See the following comments

• Comment 1
• Comment 2

Solution ideas

See the following comments

• Server deletes files (probably preferred)
• Client deletes files