Remove strict-subscriber flag (#5332)

The strict-subscriber feature flag was removed in
knative/eventing#6608 so the validation cannot
be disabled anymore. This commit adjusts the docs too.

Signed-off-by: Christoph Stäbler <cstabler@redhat.com>

Signed-off-by: Christoph Stäbler <cstabler@redhat.com>

config/nav.yml

@@ -271,7 +271,6 @@ nav:
         - New Trigger Filters: eventing/experimental-features/new-trigger-filters.md
         - KReference.Group field: eventing/experimental-features/kreference-group.md
         - Knative reference mapping: eventing/experimental-features/kreference-mapping.md
-        - Strict Subscriber: eventing/experimental-features/strict-subscriber.md
     # Eventing reference docs
       - Reference:
         - Eventing API: eventing/reference/eventing-api.md

docs/eventing/experimental-features/README.md

@@ -74,4 +74,3 @@ Knative Eventing:
 | [KReference.Group field](kreference-group.md) | `kreference-group` | Specify the API `group` of `KReference` resources without the API version. | Alpha, disabled by default |
 | [Knative reference mapping](kreference-mapping.md) | `kreference-mapping` | Provide mappings from a [Knative reference](https://github.com/knative/specs/blob/main/specs/eventing/overview.md#destination) to a templated URI. | Alpha, disabled by default |
 | [New trigger filters](new-trigger-filters.md) | `new-trigger-filters` | Enables a new Trigger `filters` field that supports a set of powerful filter expressions. | Alpha, disabled by default |
-| [Strict Subscriber](strict-subscriber.md) | `strict-subscriber` | Invalidates Subscriptions if the field `spec.subscriber` is not defined. | Alpha, disabled by default |