Refactor lastEventIsSpoiler, remove lastEvent() call that isn't needed

This is only called after we already get an event with lastEvent() so
doing it again is useless. Instead, we should refactor it to behave like
similar functions (e.g. isEventHighlighted.)

src/libneochat/neochatroom.h

@@ -212,7 +212,7 @@ public:
     [[nodiscard]] const Quotient::RoomEvent *lastEvent(std::function<bool(const Quotient::RoomEvent *)> filter = {}) const;
 
     /**
-     * @brief Convenient way to check if the last event looks like it has spoilers.
+     * @brief Convenient way to check if the event looks like it has spoilers.
      *
      * This does a basic check to see if the message contains a data-mx-spoiler
      * attribute within the text which makes it likely that the message has a spoiler
@@ -222,7 +222,7 @@ public:
      *
      * @sa lastEvent()
      */
-    [[nodiscard]] bool lastEventIsSpoiler() const;
+    [[nodiscard]] bool isEventSpoiler(const Quotient::RoomEvent *e) const;
 
     /**
      * @brief Return the notification count for the room accounting for tags and notification state.