ECMQueryQt: always use CMake target to find the qmake/qtpaths binary

This means removing the find_program() logic, since it was only useful if we don't want to make CMake spend time finding a compiler; so it was only useful for building modules that don't need a compiler at all, wallpapers, icon themes ...etc; so find_program() is only useful when it comes before the find_package() and enable_language() calls. Thanks to Christophe Giboudeaux for the explanation. This might make the build time for such modules a tiny bit longer, but it's worth it to make finding qmake/qtpaths