Remove the filestore section from ceph-volume

Remove the filestore section from ceph-volume

Filestore is no longer supported in cephadm and both the doc [1] and the
DriveGroupValidation [2] raise an exception if this method is used. This
patch removes the legacy code that is supposed to produce filestore
ceph-volume related commands.

[1] https://github.com/ceph/ceph/blob/main/doc/cephadm/adoption.rst#limitations
[2] https://github.com/ceph/ceph/blob/main/src/python-common/ceph/deployment/drive_group.py#L366-L369

Signed-off-by: Francesco Pantano <fpantano@redhat.com>