Remove $Id$ from sources

The use of $Id$ in Maven sources causes a checkout of the Git mirror to always appear modified to org.eclipse.jgit-0.11.3, which is an annoyance. Since there is no particular reason to use @version when source artifacts are strictly versioned anyway, it would be better to just remove these.

Attaching patch against current Subversion trunk which removes all occurrences of $Id$ and one $Revision. (target/generated-sources/modello contains $Revision$ $Date$ but this should not matter.)