Simplified declared dependency for javax.servlet-api

Going from Ant to Maven, we no longer need to exclude the javax.servlet-api
transitive dependency of grizzly-framework since its scope is provided
(excluding this dependency may have been a misconfiguration of Ivy).

Furthermore, upgraded javax.servlet-api from 3.1.b02 (compiled with Java 6)
to 3.1.0 (compiled with Java 7) since OpenDJ is now compiled with Java 7 minimum.