This patch enables x-ray in fireflea rooms
Fireflea rooms are notable for having all the level design drawn on layer 2 (except for elements that aren't affected by darkness, such as doors)
So aside from from removing the fireflea FX check and reverting the fireflea colour math changes during x-ray, this patch draws both layer 1 and layer 2 blocks onto the (pre-revealed) x-ray tilemap

ASM is patched with asar, e.g.:
asar "fireflea xray.asm" SM.smc

No free space used

Screenshot shows the infamous fake wall in the Lower Norfair exit path