test: don't panic on soft lockups

We can't do anything about them anyway, and most importantly this seems
to alleviate systemd/systemd-centos-ci#660, which should make the CIs
a bit less angry (at least until the issue is addressed properly).

test/test-functions

@@ -563,7 +563,6 @@ run_qemu() {
         kernel_params+=(
             "oops=panic"
             "panic=1"
-            "softlockup_panic=1"
             "systemd.wants=end.service"
         )
     fi