But this doesn't remove it from the projects review queue (or search queries, if you just use "project:mediawiki/extensions/MobileFrontend status:open").
IMHO the distinction between cleaning up personal and global dashboards is not so important. In the end, code review is performed by individuals. If each reviewer has a more relevant review queue, all reviewers will be more efficient and the backlog will decrease for everyone.
After all, we see from https://www.mediawiki.org/wiki/Gerrit/Reports/Code_review_activity that 20 reviewers do 50 % of the merging in gerrit. Some queries like those listed at https://www.mediawiki.org/wiki/Gerrit/Navigation show that over ten users have over 100 review requests in their dashboards, among those who merged something in the last month. I doubt that's efficient for them.
Nemo