Red nightshade nerfs. (#21227)

Red nightshade is an overly centralizing traitor/merc item because of
its practically zero downsides when compares to its massive benefits,
such as complete pain immunity and a whopping 1.25x damage multiplier on
all melee damage (for comparison, on an energy sword that's 42 damage
total, with 25 AP, meaning that its hits will penetrate EVERY armour in
the game). This makes melee not only insanely strong but basically
riskless in most situations, especially when combined with the esword's
parry mechanic.

Red nightshade's pain immunity has been removed in favour of a
painkiller effect of 75, more than mortaphenyl. The melee damage
multiplier has been reduced to a more sensical 1.1x.

---------

Co-authored-by: Matt Atlas <liermattia@gmail.com>

code/modules/mob/living/carbon/carbon.dm

@@ -502,8 +502,6 @@
 /mob/living/carbon/proc/can_feel_pain()
 	if (species && (species.flags & NO_PAIN))
 		return FALSE
-	if (is_berserk())
-		return FALSE
 	if ((mutations & HULK))
 		return FALSE
 	if (analgesic > 100)

code/modules/reagents/Chemistry-Reagents/Chemistry-Reagents-Toxins.dm

@@ -818,6 +818,7 @@
 		H.berserk_process()
 	M.make_jittery(20)
 	M.add_chemical_effect(CE_BERSERK, 1)
+	M.add_up_to_chemical_effect(CE_PAINKILLER, 75)
 	if(M.a_intent != I_HURT)
 		M.a_intent_change(I_HURT)
 	if(prob(3))