remove variant.hpp error

So this can be used with a Qt 5.15 build
outside of QtCreator.

Change-Id: I691687bf661be21d9c28f13a52ff5df58bb7412a
Reviewed-by: hjk <hjk@qt.io>

src/libs/utils/variant.h

@@ -29,9 +29,7 @@
     See std(::experimental)::variant.
 */
 
-// TODO: replace by #include <(experimental/)variant> depending on compiler and C++ version
 #if __cplusplus >= 201703L
-#error Please delete variant.hpp and the #else section below, then remove this error
 #include <variant>
 
 namespace Utils {