When LMDB was made a required dependency (929eccdfdc), the "LMDB" entry
was removed from features.py and the --with-lmdb flag was removed from
feature-test.c. However, the with_lmdb skip marker in mark.py and its
usage in nzd2nzf were not cleaned up. Since FEATURE_LMDB was no longer
being set, the skip condition became permanently true, silently skipping
the test on every run.
Remove the dead skip marker and update other stale references that still
described LMDB as optional (build docs, addzone test comments).
Assisted-by: Claude:claude-opus-4-7
ce9d047a5c