applets/digitalclock: return to old tooltip code
d2b33b72 replaced the old code with a Kirigami.FormLayout, which was not correct because the labels always use the app color scheme, not the Plasma color scheme, causing unreadable text when using a dark Plasma theme with a light app color scheme. This commit returns to the old code and makes a tiny fix to it to make the layout work properly (which was the reason I ported to Formlayout in the first place, so that was a wholly unnecessary change given the ability to fix the issue in another way).