Mob Destroy Refactoring (#22573)

Refactoring the entire destroy proc path from Mob Human all the way down
to Atom while trying to find the causes for the damn mob human hard
deletes. This PR comprehensively reorganizes every single stray
snowflake var used by /atom/ all the way to /mob/living/carbon/human,
and makes sure that every var that COULD store a reference, is now
cleared during the entirety of the Mob Destroy() parent hierarchy.

This may very well be the end of the lag war. 

In total, I've hunted down and cleared 39 hanging references between
/atom and /mob/living/carbon/human

---------

Signed-off-by: VMSolidus <evilexecutive@gmail.com>

code/modules/organs/blood.dm

@@ -2,8 +2,6 @@
 				BLOOD SYSTEM
 ****************************************************/
 
-/mob/living/carbon/human/var/datum/reagents/vessel	//Container for blood and BLOOD ONLY. Do not transfer other chems here.
-
 //Initializes blood vessels
 /mob/living/carbon/human/proc/make_blood()
 	if(vessel)

code/modules/organs/pain.dm

@@ -3,9 +3,6 @@
 		animate(pain, alpha = target, time = 15, easing = ELASTIC_EASING)
 		animate(pain, alpha = 0, time = 20)
 
-/mob/var/last_pain_message = ""
-/mob/var/next_pain_time = 0
-
 // message is the custom message to be displayed
 // power decides how much painkillers will stop the message
 // force means it ignores anti-spam timer