There is advice how to update php5 to php7 in https://github.com/imanseau/Cloud9-PHP7-Upgrade. Thanks a lot to imanseau.
That update removes xdebug tool, see php -v
PHP 7.0.32-4+ubuntu14.04.1+deb.sury.org+1 (cli) (built: Nov 4 2018 05:40:44) ( NTS )
Copyright © 1997-2017 The PHP Group
Zend Engine v3.0.0, Copyright © 1998-2017 Zend Technologies
with Zend OPcache v7.0.32-4+ubuntu14.04.1+deb.sury.org+1, Copyright © 1999-2017, by Zend Technologies
I would be grateful to get advice how to install xdebug in c9 PHP7 environment.