chore(kustomize): removes reference grant

The sample gateway we deploy allows route attachement from every
namespace:

```yaml
     allowedRoutes:
       namespaces:
         from: All
```

so there is no need for additional reference grant.

Follow-up of #95 (comment)

Signed-off-by: Bartosz Majsak <bartosz.majsak@gmail.com>

Author: bartoszmajsak

deployment/base/networking/kustomization.yaml

@@ -8,4 +8,3 @@ resources:
 - kuadrant.yaml
 - gateway-api.yaml
 - httproute.yaml
-- reference-grant.yaml