build,qt: Remove include directories on uninstall
* lang/qt/src/Makefile.am (uninstall-include-dirs-qt5, uninstall-include-dirs-qt6): New targets. (uninstall_include_dirs_qt5, uninstall_include_dirs_qt6): New variables. (uninstall-local): Replace with... (uninstall-hook): ...this. Add new uninstall_include_dirs_qt* variables.
We have to use uninstall-hook because uninstall-local runs before the
header files have been removed from the include folders we want to
remove.
- GnuPG-bug-id: T7205