Update classic-war.adoc

[lunicon]

Filter has no context-param element, example

  <filter>
    <filter-name>Keycloak</filter-name>
    <filter-class>org.keycloak.adapters.servlet.KeycloakOIDCFilter</filter-class>
    <init-param>
      <param-name>keycloak.config.resolver</param-name>
      <param-value>some.package.ResourceContext</param-value>
    </init-param>
  </filter>