Remove outdated warning about Postmoogle not working well with Matrix Authentication Service

This probably got fixed with Matrix Authentication Service 0.15.0 though
I'm not sure exactly which commit did it.

Ref: https://github.com/element-hq/matrix-authentication-service/releases/tag/v0.15.0

docs/configuring-playbook-matrix-authentication-service.md

@@ -55,10 +55,6 @@ This section details what you can expect when switching to the Matrix Authentica
 
 - ❌ **Some services experience issues when authenticating via MAS**:
 
-  - [Postmoogle](./configuring-playbook-bridge-postmoogle.md) works the first time around, but it consistently fails after restarting:
-
-    > cannot initialize matrix bot error="olm account is marked as shared, keys seem to have disappeared from the server"
-
 - ❌ **Encrypted appservices** do not work yet (related to [MSC4190](https://github.com/matrix-org/matrix-spec-proposals/pull/4190) and [PR 17705 for Synapse](https://github.com/element-hq/synapse/pull/17705)), so all bridges/bots that rely on encryption will fail to start (see [this issue](https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3658) for Hookshot). You can use these bridges/bots only if you **keep end-to-bridge encryption disabled** (which is the default setting).
 
 - ⚠️ [Migrating an existing Synapse homeserver to Matrix Authentication Service](#migrating-an-existing-synapse-homeserver-to-matrix-authentication-service) is **possible**, but requires **some playbook-assisted manual work**. Migration is **reversible with no or minor issues if done quickly enough**, but as users start logging in (creating new login sessions) via the new MAS setup, disabling MAS and reverting back to the Synapse user database will cause these new sessions to break.