datamodel: unbreak `dnssec: false`

It was causing an incorrect Lua line

  trust_anchors.keep_removed =

Reported on gitter a couple days ago.

added easyfix label

assigned to @amrazek

changed the description

There might be some better way here, but this change seems OK to me.

approved this merge request

added 13 commits

• 85d9b219...5c6ca32b - 12 commits from branch master
• caa3963c - datamodel: unbreak `dnssec: false`

Compare with previous version

merged

mentioned in commit 696aef6b