chore: remove stories type bookmarks (#519)

## Description
Removes stories type bookmark set, as there are going to be no
bookmarking feature for stories

## Additional Notes
<!-- Add any extra context or relevant information here. -->

## Type of Change
- [ ] Bug fix
- [ ] New feature
- [ ] Breaking change
- [ ] Refactoring
- [ ] Documentation
- [x] Chore

## Screenshots (if applicable)
<!-- Include screenshots to demonstrate any UI changes. -->
<!-- <img width="180" alt="image" src="image_url_here"> -->

lib/app/features/feed/data/models/bookmarks/bookmarks_set.c.dart

@@ -14,7 +14,7 @@ import 'package:nostr_dart/nostr_dart.dart';
 
 part 'bookmarks_set.c.freezed.dart';
 
-enum BookmarksSetType { posts, stories, videos, articles, unknown }
+enum BookmarksSetType { posts, videos, articles, unknown }
 
 @Freezed(equal: false)
 class BookmarksSetEntity with _$BookmarksSetEntity, NostrEntity implements CacheableEntity {

lib/app/features/feed/data/models/entities/post_data.c.dart

@@ -169,8 +169,6 @@ class PostData with _$PostData, EntityMediaDataMixin implements EventSerializabl
     return replyId ?? rootReplyId;
   }
 
-  bool get isStory => expiration != null;
-
   bool get hasVideo => media.values.any((media) => media.mediaType == MediaType.video);
 }
 

lib/app/features/feed/providers/bookmarks_notifier.c.dart

@@ -153,7 +153,6 @@ class BookmarksNotifier extends _$BookmarksNotifier {
   BookmarksSetType? _getBookmarkType(NostrEntity entity) {
     return switch (entity) {
       ArticleEntity() => BookmarksSetType.articles,
-      PostEntity(data: PostData(isStory: true)) => BookmarksSetType.stories,
       PostEntity(data: PostData(hasVideo: true)) => BookmarksSetType.videos,
       PostEntity() => BookmarksSetType.posts,
       _ => null,