epel-7-ppc64le chroot is broken

[praiskup]

Error: Transaction test error:
  package libgcc-4.8.5-44.el7.ppc64le does not verify: no digest
  package tzdata-2024a-1.el7.noarch does not verify: no digest
  package redhat-release-server-7.9-12.el7_9.ppc64le does not verify: no digest
  package setup-2.8.71-11.el7.noarch does not verify: no digest
  package filesystem-3.2-25.el7.ppc64le does not verify: no digest
  package basesystem-10.0-7.el7.noarch does not verify: no digest
  package subscription-manager-rhsm-certificates-1.24.54-1.el7_9.ppc64le does not verify: no digest
....

This is a follow up for #2875 where I disabled bootstrap image as it is x86 only.

[nikromen]

AI: ask on copr devel mailing list and leap team whether they need these chroots, otherwise EL7 is EOL, so we could just drop the support then.