Drop unused CMake_HAVE_CXX_UNIQUE_PTR macro

We now require C++11 `std::unique_ptr` support from the compiler,
so none of our code is conditioned on the macro.

Source/cmConfigure.cmake.h.in

@@ -24,7 +24,6 @@
 #cmakedefine CMake_HAVE_CXX_GNU_FALLTHROUGH
 #cmakedefine CMake_HAVE_CXX_ATTRIBUTE_FALLTHROUGH
 #cmakedefine CMake_HAVE_CXX_MAKE_UNIQUE
-#cmakedefine CMake_HAVE_CXX_UNIQUE_PTR
 #define CMAKE_BIN_DIR "/@CMAKE_BIN_DIR@"
 #define CMAKE_DATA_DIR "/@CMAKE_DATA_DIR@"