refactor: clean up health check and task access logic by removing unused code

backend/app/services/account_service.py

@@ -678,23 +678,6 @@ def has_task_access(user_id: int, source: str, task_id: str) -> bool:
     return row is not None
 
 
-def has_download_access(user_id: int, file_task_id: str) -> bool:
-    """Return whether one user owns a file_history entry whose download_url contains the given file task id."""
-    pattern = f"/api/download/{file_task_id}/"
-    with _connect() as conn:
-        row = conn.execute(
-            """
-            SELECT 1
-            FROM file_history
-            WHERE user_id = ? AND download_url LIKE ?
-            LIMIT 1
-            """,
-            (user_id, f"%{pattern}%"),
-        ).fetchone()
-
-    return row is not None
-
-
 # ---------------------------------------------------------------------------
 # Password reset tokens
 # ---------------------------------------------------------------------------