remove unused imports from resolver source code.

There are a few unused imports in the resolver source. It looks like they did not get removed during the last refactoring of the code.

Loggner.java
import org.osgi.service.resolver.ResolutionException;

WrappedResource.java
import org.osgi.framework.namespace.IdentityNamespace;

CopyOnWriteSet.java
import java.util.AbstractSet;