I posted this question also to the guice user group.
This is the answer I received.
The guice-3.0-no_deps.jar is a build-time artifact that's used to compile the extensions, but is not required at runtime - it's not on maven central because the Guice team didn't want people depending on this "uber-jar" by mistake. The extensions have an optional dependency to guice-3.0-no_deps.jar (so they can compile) but they also have a non-optional dependency to guice-3.0.jar for the runtime case.
Well-behaved maven plugins should see that the the no_deps dependency is optional and not throw a build error if it's missing, so this sounds like a bug in the jetty plugin. To workaround the Jetty bug you can explicitly hide this dependency as follows:
<dependency>
<groupId>com.google.inject.extensions</groupId>
<artifactId>guice-struts2</artifactId>
<version>3.0</version>
<exclusions>
<exclusion>
<groupId>com.google.inject</groupId>
<artifactId>guice</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>com.google.inject</groupId>
<artifactId>guice</artifactId>
<version>3.0</version>
</dependency>
Note that we can't do this in the original build pom because we still need the no_deps dependency when doing the original compilation.