Remove mention of required kubectl dependency.

[Algeran]

Some parts of the documentation mention that k0sctl and kubectl are required dependencies for the installation, but in fact kubectl is not required at all and k0sctl is required only for the current v4.0.0 MKE release version but 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/

1. remove all information about kubectl dependency
2. 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.

[KoryKessel-Mirantis]

Edited title to address only kubectl, and created #321 to address the k0sctl aspect for MKE 4.0.1.