Get rid of old gf, blitz, deprecated

Fixed CMakeLists accordingly and some details in the documentation.

  modified:   CMakeLists.txt
  modified:   doc/developer_manual/arrays/UserManual/slicing.rst
  modified:   doc/developer_manual/arrays_old/slicing.rst
  modified:   doc/user_manual/install/clang.rst
  modified:   pytriqs/base/CMakeLists.txt
  modified:   triqs/arrays/test/C++/CMakeLists.txt
  deleted:    triqs/deprecated
  deleted:    foreignlibs/blitz
  deleted:    pytriqs/base/gf_local
  deleted:    triqs/gf_local