Revert "Fix building akonadiprivate_obj with out of system lzma libs on macOS"

Using target_link_libraries with 'OBJECT' libraries breaks the build with older
CMake versions.

This reverts commit 2faa9de7.

src/private/CMakeLists.txt

@@ -62,7 +62,6 @@ if (WIN32)
     set(akonadiprivate_buildsources ${akonadiprivate_SRCS})
 else()
     add_library(akonadiprivate_obj OBJECT ${akonadiprivate_SRCS})
-    target_link_libraries(akonadiprivate_obj ${akonadiprivate_LIBS})
     update_include_directories(akonadiprivate_obj)
     set_target_properties(akonadiprivate_obj PROPERTIES POSITION_INDEPENDENT_CODE 1)
     add_dependencies(akonadiprivate_obj generate_protocol)