qa/suites/rados/cephadm: stop testing 18.04 + podman

The current bionice version triggers a podman/conmon bug that
truncates output, affecting both cephadm bootstrap when 'mgr dump' is
large, and teuthology 'pg dump' when it is large.

See https://tracker.ceph.com/issues/48993

Signed-off-by: Sage Weil <sage@newdream.net>

diff --git a/qa/suites/rados/cephadm/smoke/distro/ubuntu_18.04_podman.yaml b/qa/suites/rados/cephadm/smoke/distro/ubuntu_18.04_podman.yaml
deleted file mode 120000 (symlink)
index b948dd4..0000000
--- a/qa/suites/rados/cephadm/smoke/distro/ubuntu_18.04_podman.yaml
+++ /dev/null
@@ -1 +0,0 @@
-.qa/distros/all/ubuntu_18.04_podman.yaml
\ No newline at end of file

diff --git a/qa/suites/rados/cephadm/with-work/distro/ubuntu_18.04_podman.yaml b/qa/suites/rados/cephadm/with-work/distro/ubuntu_18.04_podman.yaml
deleted file mode 120000 (symlink)
index b948dd4..0000000
--- a/qa/suites/rados/cephadm/with-work/distro/ubuntu_18.04_podman.yaml
+++ /dev/null
@@ -1 +0,0 @@
-.qa/distros/all/ubuntu_18.04_podman.yaml
\ No newline at end of file

diff --git a/qa/suites/rados/cephadm/workunits/distro/ubuntu_18.04_podman.yaml b/qa/suites/rados/cephadm/workunits/distro/ubuntu_18.04_podman.yaml
deleted file mode 120000 (symlink)
index b948dd4..0000000
--- a/qa/suites/rados/cephadm/workunits/distro/ubuntu_18.04_podman.yaml
+++ /dev/null
@@ -1 +0,0 @@
-.qa/distros/all/ubuntu_18.04_podman.yaml
\ No newline at end of file