Presentation: fix g_critical about removing non-existant timer

4 jobs for BUG_presentation_duration in 4 minutes and 34 seconds
Status Job ID Name Coverage
  Build
passed #1263646
flatpak
flatpak

00:04:34

manual #1263643
allowed to fail manual
master
passed #1263644
meson

00:00:42

manual #1263645
allowed to fail manual
meson-gtk-doc