[Documentation] Remove warning box about unsupported generic RA

Hi, Generic RA will be supported component in EAP 7.1. The warning box in [1] which says that generic RA is not supported should be removed. The version of Tibco broker should be also updated from 6.3 to 8.

[1]https://doc-stage.usersys.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.1/html-single/configuring_messaging/#deploy_configure_generic_jms_resource_adapter