Removes v1beta1 AdmissionReview
Removes v1beta1 AdmissionReview

This removes v1beta1 from the possible admission review versions,
as it doesn't seem like the admission handler accepts it.

Signed-off-by: Shivam Mukhade <330299940dbe3b9a5e12a3de6ca29752465435c4@redhat.com>

tektoncd/triggers,tektoncd/triggers