Remove proxy kernel support
Created by: valentinThomazic
Related issues : https://github.com/openhwgroup/cva6/issues/1358 https://github.com/openhwgroup/cva6/issues/1638 https://github.com/openhwgroup/cva6/issues/1598 https://github.com/openhwgroup/cva6/issues/1499 https://github.com/openhwgroup/cva6/issues/1486 https://github.com/openhwgroup/cva6/issues/1222
The build flow of the pk is currently broken and unsupported by cva6.py.
The chapter about the proxy kernel in the README seems to misguide new users who try to run it following the README.
The lack of usage of the pk by the OpenHW Group team also makes it hard to support and the CVA6 repo aims primarily at hosting a platform for the documentation, RTL design and verification of CVA6 cores.
This PR aims at deleting what is already not working and does not prevent users to implement PK support in CVA6.py (which would be the right place to do so).