ceph: remove an outdated document of mon placement

Although the document describes we can't set Pod{,Anti}Affinity
to mon's placement, the current implementation permits to do so.

Signed-off-by: Satoru Takeuchi <satoru.takeuchi@gmail.com>

Documentation/ceph-cluster-crd.md

@@ -383,9 +383,6 @@ A Placement configuration is specified (according to the kubernetes PodSpec) as:
 * `tolerations`: list of kubernetes [Toleration](https://kubernetes.io/docs/concepts/configuration/taint-and-toleration/)
 * `topologySpreadConstraints`: kubernetes [TopologySpreadConstraints](https://kubernetes.io/docs/concepts/workloads/pods/pod-topology-spread-constraints/)
 
-The `mon` pod does not allow `Pod` affinity or anti-affinity. Instead, `mon`s have built-in anti-affinity with each other through the operator. The operator determines which nodes should run a `mon`. Each `mon` is then tied to a node with a node selector using a hostname.
-See the [mon design doc](https://github.com/rook/rook/blob/master/design/ceph/mon-health.md) for more details on the `mon` failover design.
-
 If you use `labelSelector` for `osd` pods, you must write two rules both for `rook-ceph-osd` and `rook-ceph-osd-prepare` like [the example configuration](https://github.com/rook/rook/blob/master/cluster/examples/kubernetes/ceph/cluster-on-pvc.yaml#L68). It comes from the design that there are these two pods for an OSD. For more detail, see the [osd design doc](https://github.com/rook/rook/blob/master/design/ceph/dedicated-osd-pod.md) and [the related issue](https://github.com/rook/rook/issues/4582).
 
 The Rook Ceph operator creates a Job called `rook-ceph-detect-version` to detect the full Ceph version used by the given `cephVersion.image`. The placement from the `mon` section is used for the Job.