Remove KDEPIM_ONLY_KLEO and icondialog copy

KDEPIM_ONLY_KLEO was a hack for Gpg4win and should
no longer be used. As far as i can tell the icondialog
copy was used in that case to avoid a KIo dependency.
KF5::IconThemes which contains kicondialog no longer
depends on KIO so this should not be needed anymore.