yum remove -y php71
This is probably not enough, you should remove everything in this SCL
yum remove php71\*
Also check you have restart the needed services (httpd, nginx, php-fpm...)
Please also notice that such vuln scanner result have no value if it use upstream "version", when package may include security fix.
Ex from php 7.1.33-22 in my repository (all known security fix from 7.4.32 are also fixed in this package)
* Tue Sep 27 2022 Remi Collet <remi@remirepo.net> - 7.1.33-22
- phar: fix #81726 DOS when using quine gzip file. CVE-2022-31628
- core: fix #81727 Don't mangle HTTP variable names that clash with ones that have a specific semantic meaning. CVE-2022-31629
* Tue Jun 07 2022 Remi Collet <remi@remirepo.net> - 7.1.33-20
- mysqlnd: fix #81719: mysqlnd/pdo password buffer overflow. CVE-2022-31626
- pgsql: fix #81720: Uninitialized array in pg_query_params(). CVE-2022-31625
etc
Of course, I recommend using a PHP upstream suported version.
I also recommend to upgrade to a more recent version of CentOS, as version is now 8 years old and close to its end of life.
Reminder: for proper repository installation and usage, follow the wizard instructions especially, if you want a single version, you don't have to install SCL designed for installation of multiple versions. And using a single version make upgrade simpler.