[Bookmarks Runner] Remove unused database parameter from query

Summary:
The query is no longer initialized for each query, just once, thus there
no longer is a need for the database parameter.

Test Plan: make

Reviewers: #frameworks, davidedmundson

Reviewed By: davidedmundson

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D15490