Remove "proxy actions" in AssetController

### Description

The `AssetController` in `Neos.Media.Browser` has a number of "proxy actions" that simply forward to other controllers (for `Tag`, `AssetCollection`, `Usage`). These should be checked and removed, as they seem to be a B/C leftover from splitting that controller.

### Affected Versions

Neos: at least 4.3 and up, but probably master is the version to clean up
