remove v1alpha4 webhooks

* as we already have webhooks for v1alpha5 we don't need webhooks for
older versions anymore.
* remove v1alpha4 from webhook mgr setup
* remove defaultIdentityRefKind const in v1alpha4

Signed-off-by: Mario Constanti <[email protected]>

Author: bavarianbidi

api/v1alpha4/identity_types.go

@@ -16,8 +16,6 @@ limitations under the License.
 
 package v1alpha4
 
-const defaultIdentityRefKind = "Secret"
-
 // OpenStackIdentityReference is a reference to an infrastructure
 // provider identity to be used to provision cluster resources.
 type OpenStackIdentityReference struct {