Drop workaround for Markup.collect_attributes()

This is fixed in valac >= 0.34.1


(cherry picked from commit a6dbce3c)

(cherry picked from commit b283d74a)
1 job for master in 17 minutes and 55 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #245858
flatpak

00:17:55