Remove duplicate osgi dependency declarations in top level pom

[janbartel]

Duplicate declarations of dependencies causes the following build warning:

> [INFO] Scanning for projects...
> [WARNING] 
> [WARNING] Some problems were encountered while building the effective model for org.eclipse.jetty.ee10:jetty-ee10-test-http2-webapp:war:12.0.0-SNAPSHOT
> [WARNING] 'dependencyManagement.dependencies.dependency.(groupId:artifactId:type:classifier)' must be unique: org.osgi:osgi.annotation:jar -> version ${osgi-annotation-version} vs ${org.osgi.annotation.version} @ org.eclipse.jetty:jetty-project:12.0.0-SNAPSHOT, /home/janb/src/jetty-eclipse/jetty-12.0.x/pom.xml, line 1681, column 19
> [WARNING] 'dependencyManagement.dependencies.dependency.(groupId:artifactId:type:classifier)' must be unique: org.osgi:org.osgi.util.promise:jar -> version ${osgi-util-promise-version} vs ${org.osgi.util.promise.version} @ org.eclipse.jetty:jetty-project:12.0.0-SNAPSHOT, /home/janb/src/jetty-eclipse/jetty-12.0.x/pom.xml, line 1691, column 19
> [WARNING] 
> [WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
> [WARNING] 
> [WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
>