nip10: consolidate event_ref logic into ThreadReply

These are overlapping concepts, lets slowly get rid of EventRef

Signed-off-by: William Casarin <jb55@jb55.com>

damus/Util/EventCache.swift

@@ -169,7 +169,7 @@ class EventCache {
         var ev = event
         
         while true {
-            guard let direct_reply = ev.direct_replies(keypair).last,
+            guard let direct_reply = ev.direct_replies(keypair),
                   let next_ev = lookup(direct_reply), next_ev != ev
             else {
                 break
@@ -183,7 +183,7 @@ class EventCache {
     }
     
     func add_replies(ev: NostrEvent, keypair: Keypair) {
-        for reply in ev.direct_replies(keypair) {
+        if let reply = ev.direct_replies(keypair) {
             replies.add(id: reply, reply_id: ev.id)
         }
     }

damus/Util/ReplyCounter.swift

@@ -39,7 +39,7 @@ class ReplyCounter {
         
         counted.insert(event.id)
         
-        for reply in event.direct_replies(keypair) {
+        if let reply = event.direct_replies(keypair) {
             if event.pubkey == our_pubkey {
                 self.our_replies[reply] = event
             }