DetectUnsupportedVersion is somewhat uncomfortable, complex and inefficient
function to use. It takes an entire YAML document as bytes, splits it up to
byte slices of the different YAML sub-documents and group-version-kinds and
searches through those to detect an unsupported kubeadm config. If such config
is detected, the function returns an error, if it is not (i.e. the normal
function operation) everything done so far is discarded.

This could have been acceptable, if not the fact, that in all cases that this
function is called, the YAML document bytes are split up and an iteration on
GVK map is performed yet again. Hence, we don't need DetectUnsupportedVersion
in its current form as it's inefficient, complex and takes only YAML document
bytes.

This change replaces DetectUnsupportedVersion with ValidateSupportedVersion,
which takes a GroupVersion argument and checks if it is on the list of
unsupported config versions. In that case an error is returned.
ValidateSupportedVersion relies on the caller to read and split the YAML
document and then iterate on its GVK map checking if the particular
GroupVersion is supported or not.
Signed-off-by: Rostislav M. Georgiev <rostislavg@vmware.com>