Improve logging for gradle resolver

[johnynek]

This does two main things:

1. removes an annoying println in our logs about using VersionResolver. We have configured to use the "highest" conflict resolution. We don't need to println every time that runs. If we want to error, there is a VersionConflictPolicy for that: Fixed. I moved that println to a debug setting (which we can select with --verbosity debug to bazel-deps).
2. adds a bit more info logging to make sure deleted edges were being seen.