[PlacesItemModelTest] Revert last two commits

Commit c527dc21 proves that on the CI sometimes the `QAbstractItemModel::dataChanged`
signal is not being emitted at all (build #208 failed because the test timed out).

KFilePlacesModel emits `dataChanged()` in the `_k_reloadBookmarks()`
slot only when it's called after the KBookmarkManager emits the `changed()` signal.

And the `changed()` signal is emitted after KDirWatch emits the
`created` signal.

On the CI server kdirwatch is probably not reliable, which would explain
why the test randomly fails.