Remove dead code identified by deadcode tool (#37271)

Ran [`deadcode`](https://pkg.go.dev/golang.org/x/tools/cmd/deadcode)
(`-test ./...`) to find functions, methods and error types unreachable
from any call path (including tests), and removed the truly-dead ones.

Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

models/activities/action_list.go

@@ -282,9 +282,3 @@ func GetFeeds(ctx context.Context, opts GetFeedsOptions) (ActionList, int64, err
 
 	return actions, count, nil
 }
-
-func CountUserFeeds(ctx context.Context, userID int64) (int64, error) {
-	return db.GetEngine(ctx).Where("user_id = ?", userID).
-		And("is_deleted = ?", false).
-		Count(&Action{})
-}