Deleted 4 old and low rated notes

Following were the 4 notes with a rating less than -5 and
are older than 1 year.

These notes represented 0.0% of the 16900 total user notes,
and have now been removed.

Rating | Note
-------+---------------------------------------------------------
   -6  | https://php.net/manual/en/function.isset.php#69025
   -6  | https://php.net/manual/en/function.rrd-fetch.php#113153
   -6  | https://php.net/manual/en/jsonserializable.jsonserialize.php#123382
   -6  | https://php.net/manual/en/function.odbc-connect.php#71570