Leave out builds on ppc64le for now

Those are very often taking longer than 50 mins, requiring multiple tries
to complete on Travis CI. It's unclear if the ppc64le runners are just
overbooked or generally slower than the arm64 ones (unlikely).

.travis.yml

@@ -24,9 +24,11 @@ jobs:
     - &run_tests
       # Template; subsequent uses modify 'env'
       arch:
-        - ppc64le
+#        - ppc64le
+        - arm64
       env:
-        - IMAGE=ppc64le/rockylinux:9 TASK=tests COMPONENTS=udt,myproxy,ssh
+#        - IMAGE=rockylinux:9 TASK=tests COMPONENTS=udt,myproxy,ssh
+        - IMAGE=rockylinux:8 TASK=tests COMPONENTS=udt,myproxy,ssh
       stage: test
       services:
         - docker
@@ -39,20 +41,20 @@ jobs:
       script:
       - travis-ci/setup_tasks.sh
 
-    - <<: *run_tests
-      arch:
-        - arm64
-      env:
-        - IMAGE=arm64v8/rockylinux:8 TASK=tests COMPONENTS=udt,myproxy,ssh
+#    - <<: *run_tests
+#      arch:
+#        - arm64
+#      env:
+#        - IMAGE=rockylinux:8 TASK=tests COMPONENTS=udt,myproxy,ssh
 
-    - <<: *run_tests
-      arch:
-        - ppc64le
-      env:
-        - IMAGE=ppc64le/rockylinux:9 TASK=tests COMPONENTS=gram5
+#    - <<: *run_tests
+#      arch:
+#        - ppc64le
+#      env:
+#        - IMAGE=rockylinux:9 TASK=tests COMPONENTS=gram5
 
     - <<: *run_tests
       arch:
         - arm64
       env:
-        - IMAGE=arm64v8/rockylinux:8 TASK=tests COMPONENTS=gram5
+        - IMAGE=rockylinux:8 TASK=tests COMPONENTS=gram5