A plethora of Destroy() fixes - return qdel hints and clean stuff up.

code/modules/mob/dead/observer/observer.dm

@@ -132,7 +132,7 @@ var/global/list/image/ghost_sightless_images = list() //this is a list of images
 		qdel(ghostimage)
 		ghostimage = null
 		updateallghostimages()
-	..()
+	return ..()
 
 /mob/observer/dead/Topic(href, href_list)
 	if (href_list["track"])

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

@@ -110,10 +110,8 @@
 	if(isrobot(loc))
 		var/mob/living/silicon/robot/borg = loc
 		borg.mmi = null
-	if(brainmob)
-		qdel(brainmob)
-		brainmob = null
-	..()
+	qdel_null(brainmob)
+	return ..()
 
 /obj/item/device/mmi/radio_enabled
 	name = "radio-enabled man-machine interface"