e2e: drop test depending on CentOS 7

[dtrudg]

Description of the Pull Request (PR):

CentOS 7 has gone end of life. Various infrastructure like the mirrorlist is no longer available:

https://lists.centos.org/hyperkitty/list/devel@lists.centos.org/thread/EGOA27SGN7W7ASFFFBNUZJ5BXSFT4NKX/

Drop the regression test for 5250, which depends on CentOS7 and is failing due to the retirement of the mirrorlist.

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