Update Keycloak_Integration.adoc

The "Using Keycloak with WildFly Elytron" section in the WildFly documentation is out of date since the elytron-oidc-client subsystem is now used instead. The following changes should be made to this page:

• The first paragraph should be reworded to something like:
  • The ability to secure applications using OpenID Connect is
    provided by the elytron-oidc-client subsystem. For details on how to secure applications deployed to WildFly with OpenID Connect using Keycloak as the OpenID provider, see the Elytron OIDC Client documentation.

• The Zip Installation, Galleon installation, and Bootable Jar sections can all be deleted.