The HIG now states that should only be used for non-default, uncommon, unusual, or unexpected statuses: https://hig.kde.org/components/assistance/emblem.html
Accordingly, we should only show an emblem when a disk is unmounted, not when it's mounted. Being mounted is the expected status for a disk; being unmounted-but-visible-anyway is what's unusual and deserves an emblem.
As an added bonus, this hugely improves the look of the Places panel by default.
Closes T9740