migrate repository converter to new repository API

the use of repository-layer and model need to be removed.

In the process, the role of the repository converter module may need to be revisited. Currently it is only for maven 1 -> maven 2 conversion. This may be of limited utility to retain, depending on the complexity of retaining it. It may also be better stored in maven 1.x plugin (ie, it would be 1.x -> metadata repository rather than a specific 1.x -> 2.x conversion to support other formats), or there may be a desire to have a more generalised conversion utility with hooks for repository specifics.