add route to remove playlist banner

app/db/sqlite/playlists.py

@@ -177,6 +177,13 @@ class SQLitePlaylistMethods:
         with SQLiteManager(userdata_db=True) as cur:
             cur.execute(sql, (pos, playlistid))
 
+    @staticmethod
+    def remove_banner(playlistid: int):
+        sql = """UPDATE playlists SET image = NULL WHERE id = ?"""
+
+        with SQLiteManager(userdata_db=True) as cur:
+            cur.execute(sql, (playlistid,))
+
     @staticmethod
     def remove_tracks_from_playlist(playlistid: int, tracks: list[dict[str, int]]):
         """