nwc: remove requests from postbox

Since these are ephemeral events, there will never be command results,
so we need to remove them manually on NWC responses or else it will keep
trying to send them.

We should probably handle this for all ephemeral events in the postbox
somehow. We probably shouldn't use the postbox for ephemeral events
without response events.

damus/Util/PostBox.swift

@@ -104,16 +104,18 @@ class PostBox {
         remove_relayer(relay_id: relay_id, event_id: cr.event_id)
     }
     
-    func remove_relayer(relay_id: String, event_id: String) {
+    @discardableResult
+    func remove_relayer(relay_id: String, event_id: String) -> Bool {
         guard let ev = self.events[event_id] else {
-            return
-        }
-        ev.remaining = ev.remaining.filter {
-            $0.relay != relay_id
+            return false
         }
+        let prev_count = ev.remaining.count
+        ev.remaining = ev.remaining.filter { $0.relay != relay_id }
+        let after_count = ev.remaining.count
         if ev.remaining.count == 0 {
             self.events.removeValue(forKey: event_id)
         }
+        return prev_count != after_count
     }
     
     private func flush_event(_ event: PostedEvent, to_relay: Relayer? = nil) {
@@ -147,3 +149,5 @@ class PostBox {
         }
     }
 }
+
+