RFR 8068938: javax.script package description should specify use of ServiceLoader

[Sundararajan Athijegannathan]

Please review http://cr.openjdk.java.net/~sundar/8068938/webrev.00/ for 
https://bugs.openjdk.java.net/browse/JDK-8068938

This is a doc-only change to mention that ScriptEngineFactory instances 
are loaded using java.util.ServiceLoader API and avoid wording on 
META-INF/services [ which is just one impl. mechanism used by 
ServiceLoader ]. This will allow the ScriptEngineFactory implementations 
to be deployed as modules without the service configuration file.

Thanks,
-Sundar