Validatable config should skip obsolete modules

At the moment there's only one obsolete module help_topics

So the fix is

- ls core/modules | xargs vendor/bin/drush pm:install --yes
+ ls core/modules | grep -v help_topics | xargs vendor/bin/drush pm:install --yes

Bur when more modules will be added makes sense to grep "obsolete" status from info file

RTBC +1

Committing this from needs review because head is broken.

Committed/pushed to 11.x and cherry-picked to 10.3.x, thanks!

Automatically closed - issue fixed for 2 weeks with no activity.