SERVER-96097 Update rhel8 s390x to new legacy fleet on mdb 7.0 (#30967)

GitOrigin-RevId: cdaf999617148b1b15e1e84ca237ff8e77fcb97e

Author: zackwintermdb

etc/evergreen_yml_components/variants/ibm.yml

@@ -86,7 +86,7 @@ buildvariants:
 - name: enterprise-rhel-83-s390x
   display_name: Enterprise RHEL 8.3 s390x
   run_on:
-  - rhel83-zseries-small
+  - rhel8-zseries-large-legacy
   cron: "0 4 * * 0"
   stepback: false
   expansions:
@@ -120,8 +120,6 @@ buildvariants:
     compile_variant: enterprise-rhel-83-s390x
   tasks:
   - name: small_compile_test_and_package_serial_no_unittests_TG
-    distros:
-    - rhel83-zseries-large
   - name: .aggregation .common
   - name: audit
   - name: .auth !.multiversion !.jscore