Remove ProblemReport ProblemType enum altogether

It only has one value, so there's no point keeping it hanging around.
5 jobs for <span class="ref-name">wip/problem-report-cleanup</span> in 33 minutes and 18 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #251875
fedora

00:09:16

passed #251876
ubuntu

00:12:56

 
  Test
passed #251877
flatpak

00:19:18

 
  Deploy
passed #251878
review

00:00:28

passed #251879
allowed to fail manual
stop_review

00:00:33