[ci skip] DocBlocks for DB drivers' utility classes

Partially fixes issue #1295.
diff --git a/system/database/drivers/ibase/ibase_utility.php b/system/database/drivers/ibase/ibase_utility.php
index 06de677..5eb209a 100644
--- a/system/database/drivers/ibase/ibase_utility.php
+++ b/system/database/drivers/ibase/ibase_utility.php
@@ -35,10 +35,8 @@
  */
 class CI_DB_ibase_utility extends CI_DB_utility {
 
-	protected $_list_databases	= FALSE;
-
 	/**
-	 * Interbase/Firebird Export
+	 * Export
 	 *
 	 * @param	string	$filename
 	 * @return	mixed