If you try to delete a LAN server, the game will crash.

STEPS TO REPRODUCE:
1: Have someone on your network start a LAN Server
2: Select that server in the multiplayer menu (Don't login, just highlight)
3: Press Delete
The game will crash

Possible solution:
Minecraft can tell if its a LAN server. If you highlight a LAN server, you should make it grey out the delete button.