Remove unused oldProvider property in _rs2serialize()

Property was assigned but not referenced anywhere in the code base,
except for a mention in the 4.x changelog from 2005.

Fixes #957

adodb-csvlib.inc.php

@@ -80,7 +80,6 @@ function _rs2serialize(&$rs,$conn=false,$sql='')
 		$rs2 = new $class(ADORecordSet::DUMMY_QUERY_ID);
 		$rs2->timeCreated = $rs->timeCreated; # memcache fix
 		$rs2->sql = $rs->sql;
-		$rs2->oldProvider = $rs->dataProvider;
 		$rs2->InitArrayFields($rows,$flds);
 		$rs2->fetchMode = $savefetch;
 		return $line.serialize($rs2);