applets/devicenotifier: use standard section header
Reason for the change
No need for a custom header here when we have a standard one. Consistency++
Screenshots or screen recordings
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Bugs fixed
Additional information
I'm not super thrilled with the whitespace before the first section header. However this is built into the component itself (which lives in libplasma, not here) and needs to be fixed there. I tried for a while to do so by checking whether there was a previous section, but couldn't find a way to make it work.