Thermite no longer has 80% chance to burn forever

A stray line from the old meteorhit code wandered in. Since this proc
runs once per thermite activation, there was only 20% chance to run the
code that deletes the overlay and turns the thermitedness stat to False.
Merge pull request #100 from Profakos/thermiteFix

Thermite no longer has 80% chance to burn forever