The production guide gives the following guidance about disabling the bundled Keycloak components:

Because you will be using an external/standalone Keycloak server, it is useful to disable the Keycloak components that are bundled with the apiman quickstart. To do that, make the following modification to the standalone-apiman.xml file:
<subsystem xmlns="urn:jboss:domain:keycloak:1.0">
  <auth-server name="main-auth-server">
    <enabled>false</enabled>
    <web-context>auth</web-context>
  </auth-server>
</subsystem>

When I start the server after upgrading from 1.2.0.Final, and comparing the standalone-apiman.xml config file with the old one, I get:

20:46:49,393 ERROR [org.jboss.as.server] (Controller Boot Thread) WFLYSRV0055: Caught exception during boot: org.jboss.as.controller.persistence.ConfigurationPersistenceException: WFLYCTL0085: Failed to parse configuration

at org.jboss.as.controller.persistence.XmlConfigurationPersister.load(XmlConfigurationPersister.java:131) [wildfly-controller-1.0.2.Final.jar:1.0.2.Final]

…

Caused by: javax.xml.stream.XMLStreamException: Unknown keycloak-server subsystem tag: auth-server

Any idea what this configuration should look like now?