[TECH DEBT] Drop CentOS 7 due to EOL in June 2024

[ScriptAutomate]

CentOS 7 is EOL June 2024:

RHEL 7 reaches End of Maintance on June 30, 2024. After June 30, 2024, there will be no updates published for CentOS Linux 7.

References:

• https://blog.centos.org/2023/04/end-dates-are-coming-for-centos-stream-8-and-centos-linux-7/
• https://www.redhat.com/en/topics/linux/centos-linux-eol
• https://www.redhat.com/en/technologies/linux-platforms/enterprise-linux/rhel-7-end-of-maintenance

Drop from the Salt test suite to both reduce cost, reduce maintainership burden, and to be in line with CentOS 7 EOL and RHEL 7 EOM policies.