Quick Open: Remove "file:///" prefix from file paths

Summary:
In the second column, remove all "file:///" prefixes from the file paths.

Screenshot BEFORE:

(Note, that the screenshot was taken at a time where the file paths in the upper section where not bold (before d6e38c0cbd3d6d7f7658862757b8c33db4322d7a). Now, the items in the first and second column are both bold)

AFTER:

Reviewers: Kate, cullmann

Reviewed By: Kate, cullmann

Subscribers: cullmann, kfunk, gregormi, broulik, dhaumann, tcanabrava, kwrite-devel

Tags: Kate

Differential Revision: https://phabricator.kde.org/D16204