[refactor] Hide Protobuf Warning when not needed

Projects/paraview.cmake

 set(pv_cmake_options "")
 find_package(Protobuf)
-if (Protobuf_FOUND)
+if (Protobuf_FOUND AND NOT VTK_USE_SYSTEM_PROTOBUF)
   message(MESSAGE "Found a system-wide Protobuf library, tell VTK to use it to avoid runtime version mismatch")
   set(VTK_USE_SYSTEM_PROTOBUF ON CACHE BOOL "Tell paraview to use the system-wide Protobuf that CMake found, to avoid runtime version mismatch.")
   list(APPEND pv_cmake_options "-DVTK_USE_SYSTEM_PROTOBUF:BOOL=${VTK_USE_SYSTEM_PROTOBUF}" )