plans/ci.fmf we had here wasn't particularly useful, it duplicated
osci_compose_gate (see gating.yaml).
The testing configuration in c9s is at the moment in a better shape,
thanks to RHEL-69756. Let's align c10s with c9s.
Remove the gating tests from here and use the tests from
https://src.fedoraproject.org/tests/gcc
There's more of them there, they are are more up-to-date,
maintained by RHEL QA staff and re-used in other downstreams
(CentOS Stream, RHEL, RHIVOS).
