You can use regex to selecting target part of string and run it in preg_replace()
.
$url = "http://aaa-aaaa.com/bbbb-bbbbbbbbbb-2/it/clients/";
echo preg_replace("@(.*)\w{2}/([^/]+/)$@", "$1$2", $url);
See result of code in demo
solved Remove only 3 characters after a specific string