[ci-management] Combine qemux86-64 and intel-corei7 build once SPEC-2931 is done

SPEC-2931 merges the qemux86-64 and intel builds into one.

Reflect this change in ci-management and move the intel build to replace qemux86-64 in the pipeline (CIB phase).

For CIBT phase, keep both CIBT-qemux86-64 and CIBT-intel-corei7-64 and adapt releng scripts for qemux86-64 to use the intel build artifacts.

We'll likely have to backport this to halibut (SPEC-2931) .