Since Moodle 2.0, the $DB->delete_records() method always return true. If some problem is found, it throws exception.

So code like this:

if ($DB->delete_records($table, $params)) {

    // Conditional code here

...

Has no sense at all. Review all the current uses and change them to be linear / add extra checks if needed.

Tip: grep -r "if" * | grep delete_records

Ciao