Remove krew support (#11824)

* Remove krew installation support

Krew is fundamentally to install kubectl plugins, which are eminently a
client side things.
It's also not difficult to install on a client machine.

* Remove krew cleanup

roles/kubespray-defaults/defaults/main/main.yml

@@ -411,7 +411,6 @@ dashboard_enabled: false
 
 # Addons which can be enabled
 helm_enabled: false
-krew_enabled: false
 registry_enabled: false
 metrics_server_enabled: false
 enable_network_policy: true
@@ -746,9 +745,6 @@ proxy_disable_env:
   https_proxy: ''
   no_proxy: ''
 
-# krew root dir
-krew_root_dir: "/usr/local/krew"
-
 # sysctl_file_path to add sysctl conf to
 sysctl_file_path: "/etc/sysctl.d/99-sysctl.conf"