Refactor import paths in chart scripts and update database

- Updated import statements in `bitcoin_m2_chart.py` and `custom_chart.py` to use a simplified path for `fetch_series_db` and `save_figure`.
- Removed obsolete `chart.png` file from outputs.
- Made changes to `fred.db`, indicating updates to the database content.

scripts/custom_chart.py

@@ -17,8 +17,7 @@ from typing import Iterable
 import matplotlib.dates as mdates
 import matplotlib.pyplot as plt
 import pandas as pd
-from scripts.common import fetch_series_db, save_figure
-
+from common import fetch_series_db, save_figure
 
 def fetch_series_multi(
     series: Iterable[str],