Make sure that old URLs do not appear duplicated in places model

Summary:
BUG: 389401

KIO model now provides Baloo URLs; we need to remove the old ones
created by Dolphin places model

BUG: 387888
Depends on D9332

Test Plan: unit test

Reviewers: mwolff, #dolphin, ngraham, elvisangelaccio

Reviewed By: #dolphin, ngraham, elvisangelaccio

Subscribers: elvisangelaccio, broulik, ervin, ngraham, #dolphin

Differential Revision: https://phabricator.kde.org/D9333