[Timeline KIO] Don't announce that we can write
It's read-only, trying to copy raises an "unsupported action" error.
All files in here are linked as local files, so opening a file will actually redirect to the real location and so editing files works fine without the worker being marked as writable.
For system/dolphin!346 (merged) so it doesn't let me drop files on timeline URLs
- Was still able to open a file in Kolourpaint and edit it