Remove redundancy when adding Tags and Comments in Dolphin

Summary:
BUG: 308392

Replaced: "Tags: Add Tags.." and "Comments: Add Comments..." with "Tags: Add..." and "Comments: Add..."

Reviewers: broulik, #dolphin, #kde_applications

Reviewed By: broulik

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D7667