Kubernetes release .tar.gz no longer provides binaries. So the existing
instructions are invalid (#2815).
User has to get the .tar.gz file and then run a script, only to download them
from storage.googleapis.com/kubernetes-release. That's already what's documented
in the "install via curl" section.
Therefore deleting "Extract kubectl from Release .tar.gz" section.
Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>