removes add_gas() and assert_gas(). next up: do further testing with garbage_collect() present and not present

code/modules/assembly/bomb.dm

@@ -143,7 +143,6 @@
 	return
 
 /obj/item/tank/proc/ignite()	//This happens when a bomb is told to explode
-	air_contents.assert_gases(/datum/gas/plasma, /datum/gas/oxygen)
 	var/fuel_moles = air_contents.gases[/datum/gas/plasma] + air_contents.gases[/datum/gas/oxygen]/6
 	air_contents.garbage_collect()
 	var/datum/gas_mixture/bomb_mixture = air_contents.copy()