Merge pull request #11882 from Putnam3145/fix-deleting-objectives

Makes objectives clean theirselves up properly

code/game/gamemodes/objective.dm

@@ -19,6 +19,15 @@ GLOBAL_LIST_EMPTY(objectives)
 	if(text)
 		explanation_text = text
 
+/datum/objective/Destroy(force, ...)
+	GLOB.objectives -= src
+	if(owner)
+		for(var/datum/antagonist/A in owner.antag_datums)
+			A.objectives -= src
+	if(team)
+		team.objectives -= src
+	. = ..()
+
 /datum/objective/proc/get_owners() // Combine owner and team into a single list.
 	. = (team && team.members) ? team.members.Copy() : list()
 	if(owner)