Update comments around built in trust anchors
requested to merge 3012-begin-end-dnssec-managed-keys-in-bin-named-config-c-are-mismatched-v9_16 into v9_16
The comments now say "# BEGIN TRUST ANCHORS" and "# END TRUST ANCHORS".
(cherry picked from commit 43a7f3f5)
Closes #3012 (closed)