Draft: Cmake: Remove _KF from LIBEXECDIR

KDE_INSTALL_LIBEXECDIR_KF => KDE_INSTALL_LIBEXECDIR KDE_INSTALL_FULL_LIBEXECDIR_KF => KDE_INSTALL_FULL_LIBEXECDIR

_KF suffix have been outdated for some time.

This may explain this error in Windows: https://discuss.kde.org/t/cannot-delete-with-dolphin-in-windows/13907/3

Ref at: https://invent.kde.org/frameworks/extra-cmake-modules/-/blob/master/kde-modules/KDEInstallDirs6.cmake?ref_type=heads