remove container_exec_cmd_mgr fact

Iterating over all monitors in order to delegate a `
{{ container_binary }}` fails when collocating mgrs with mons, because
ceph-facts reset `container_exec_cmd` to point to the first member of
the monitor group.

The idea is to force `container_exec_cmd` to be reset in ceph-mgr.
This commit also removes the `container_exec_cmd_mgr` fact.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1791282



Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 8dcbcecd)