Revert accidential merge of !16.

This adresses #26 (closed).

Revert "Merge remote-tracking branch 'refs/remotes/core/feature/vc' into patches"

This reverts commit 68d8b5a5, reversing changes made to e8d207bb.

cmake/modules/AddVcFlags.cmake

-# Defines the functions to use VC
-#
-# .. cmake_function:: add_dune_vc_flags
-#
-#    .. cmake_param:: targets
-#       :positional:
-#       :single:
-#       :required:
-#
-#       A list of targets to use VC with.
-#
-
-function(add_dune_vc_flags _targets)
-  if(Vc_FOUND)
-    foreach(_target ${_targets})
-      target_link_libraries(${_target} ${Vc_LIBRARIES})
-      target_compile_options(${_target} PUBLIC ${Vc_ALL_FLAGS})
-      target_include_directories(${_target} SYSTEM PUBLIC ${Vc_INCLUDE_DIR})
-    endforeach(_target ${_targets})
-  endif(Vc_FOUND)
-endfunction(add_dune_vc_flags)
-
-if(Vc_FOUND)
-  dune_register_package_flags(COMPILE_OPTIONS "${Vc_ALL_FLAGS}"
-                              LIBRARIES "${Vc_LIBRARIES}"
-                              INCLUDE_DIRS "${Vc_INCLUDE_DIR}")
-endif(Vc_FOUND)
-set(HAVE_VC ${Vc_FOUND})