Port away from deprecated KIO::UDSEntry::insert()

Summary:
Using replace for DesktopProtocol::prepareUDSEntry(), as we have
no guarantee that certain fields are not set elsewhere in the call chain

Test Plan: Both kio-slave still work

Reviewers: #plasma, chinmoyr

Reviewed By: chinmoyr

Subscribers: chinmoyr, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D18632