CI: remove s390x builds from Packit configuration

The related CI jobs frequently take more than an hour to start
and nobody uses the `s390x` builds of `csmock` anyway.

Author: kdudka

.packit.yaml

@@ -27,11 +27,9 @@ jobs:
       targets:
           - epel-all-aarch64
           - epel-all-ppc64le
-          - epel-all-s390x
           - epel-all-x86_64
           - fedora-all-aarch64
           - fedora-all-ppc64le
-          - fedora-all-s390x
           - fedora-all-x86_64
 
     # EPEL tests