notificationspopup: Fix source not found warning

If the notification is visible, it means that the timeout is already
finished. In that case, source_remove does not need to be called.


(cherry picked from commit 51df37f9)
3 jobs for cherry-pick-51df37f9 in 7 minutes and 18 seconds (queued for 13 seconds)
Status Job ID Name Coverage
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passed #22379
pep8

00:02:03

passed #22378
pyflakes

00:02:32

 
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passed #22380
build

00:04:46