Make Tomcat 6 and Jetty 6 and 7 specific configuration obsolete

According to the documentation:
http://docs.jboss.org/weld/reference/1.1.0.Final/en-US/html_single/#d0e5286

We have to add extra configuration files to deploy to certain appservers and certain versions.
But the existence of those files can sometimes create issues on other appservers.
For example, jetty 6 needs an WEB-INF/jetty-env.xml file (and Jetty 7 needs another version of that file).
"Maven profiles" are not a solution, see WELD-984.

Since weld-servlet's bootstrap actually detects what appserver and what version is in play, it should be thoroughly investigated if weld can't do that for us
and only configure the content of those extra files if the correct appserver/version is being used.