Drop canal network_plugin (#10100)

According to the canal github[1] the repo is not maintained over 5 years.
In addition, the README says
```
  Originally, we thought we might more deeply integrate the two projects
  (possibly even going as far as a rebranding!). However, over time it
  became clear that that wasn't really necessary to fulfil our goal of
  making them work well together. Ultimately, we decided to focus on
  adding features to both projects rather than doing work just to
  combine them.
```
So it is difficult to support canal by Kubespray at this situation.

[1]: https://github.com/projectcalico/canal

inventory/sample/group_vars/k8s_cluster/k8s-net-canal.yml

@@ -1,10 +0,0 @@
-# see roles/network_plugin/canal/defaults/main.yml
-
-# The interface used by canal for host <-> host communication.
-# If left blank, then the interface is choosing using the node's
-# default route.
-# canal_iface: ""
-
-# Whether or not to masquerade traffic to destinations not within
-# the pod network.
-# canal_masquerade: "true"