Revert "denylist: skip PXE tests on ppc64le"

This reverts commit 5e5cbec.

Those tests should work now with the workaround added in
coreos/coreos-assembler#3661.

kola-denylist.yaml

@@ -55,12 +55,5 @@
   osversion:
     - c9s
 
-# Other failing tests
-- pattern: pxe-*.ppcfw
-  tracker: https://github.com/coreos/coreos-assembler/issues/3370
-  # nb: testiso doesn't read this, so it's just for consistency
-  arches:
-    - ppc64le
-
 - pattern: iso-offline-install-iscsi.bios
   tracker: https://github.com/coreos/fedora-coreos-tracker/issues/1638