Remove mention of required k0stcl dependency

[KoryKessel-Mirantis]

Some parts of the documentation mention that k0sctl as a required dependency for the installation, but in fact k0sctl is required only for the current v4.0.0 MKE release version and will not be for the upcoming v4.0.1 release.

MirantisContainers/mke-release#15

On these 2 pages:

https://docs.mirantis.com/mke-docs/docs/getting-started/install-mke-cli/
https://docs.mirantis.com/mke-docs/docs/migrate-from-mke-3/

Since MKE v4.0.1 (not released yet), the k0sctl dependency is no longer required, and the install.sh script will not install it automatically either.