PlacesItemModel: remove redundant set of properties

Summary:
The text, icon and url properties are already set in
PlacesItem::setBookmark(), so there is no need to set them here.

The OnlyInApp property is part of the KBookmark object that we are
going to set to the place item, so there is no need to set it here either.

Test Plan:

• Open both dolphin and the Plasma file dialog in some app
• Edit the text, url, icon and the "Only show when using this application" checkbox in some place item from the file dialog
• Check whether the place in dolphin keeps getting updated accordingly

Reviewers: Dolphin, meven, ngraham

Subscribers: kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D25230