Revert "Move cern.ch.conf to cvmfs-keys and add egi.eu and opensciencegrid.org there"

This reverts commit 29e6d1efdac6291e4ec78191a9d5af32222bdfd7.
Revert "Add egi.eu and openscience.org configurations, including server ordering"

This reverts commit b3b94a12fe5b76e6945944ecb00cbcfd232d4266.
Revert "Move cvmfs-keys files from the mount directory to their own directory"

This reverts commit 6fd9616339aed9d22c9b68a078c17cd1d68584c2.
Add egi.eu and opensciencegrid.org keys & config