Remove contents of Phys following move to Rec
This follows up on Rec!2637 (merged) by removing the contents of Phys with the exception of release notes.
A README with some explanations is added: https://gitlab.cern.ch/lhcb/Phys/-/blob/clean-master/README.md.
Closes the big task #19 (closed).
Edited by Eduardo Rodrigues