Avoid creating obsolete gateway-api namespace
Avoid creating obsolete gateway-api namespace

Small issue in commit 08eae8a - both manifests create the required
namespace and we only renamed gateway-api to gateway-system in one of
them.

Before:

  namespace/gateway-system created
  validatingwebhookconfiguration.admissionregistration.k8s.io/gateway-api-admission created
  service/gateway-api-admission-server created
  deployment.apps/gateway-api-admission-server created
  namespace/gateway-api created

after:

  namespace/gateway-system created
  validatingwebhookconfiguration.admissionregistration.k8s.io/gateway-api-admission created
  service/gateway-api-admission-server created
  deployment.apps/gateway-api-admission-server created
  namespace/gateway-system unchanged

istio/gateway-api,istio/gateway-api,istio/gateway-api