task/kernel: drop removal of old kernels
task/kernel: drop removal of old kernels

1- this isn't necessary anymore with fog
2- the package-cleanup --oldkernels option doesn't exist in el8

Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@redhat.com>

dmick/teuthology,SUSE/teuthology,ceph/teuthology,ktdreyer/teuthology,SUSE/teuthology,SUSE/teuthology,ktdreyer/teuthology,dmick/teuthology,dmick/teuthology,ceph/teuthology