Deletes source code for deprecated OFS plugin

xroot_plugins/CMakeLists.txt

xroot_plugins/CmdLineTool.cpp

xroot_plugins/CmdLineTool.hpp

xroot_plugins/ListArchiveFilesCmd.cpp

xroot_plugins/ListArchiveFilesCmd.hpp

xroot_plugins/XrdCtaDir.cpp

xroot_plugins/XrdCtaDir.hpp

xroot_plugins/XrdCtaFile.cpp

xroot_plugins/XrdCtaFile.hpp

xroot_plugins/XrdCtaFilesystem.cpp

xroot_plugins/XrdCtaFilesystem.hpp

xroot_plugins/cta-frontend-xrootd.conf