Verify possibly-retired InfluxDB `_internal` fields: httpd.valuesWrittenOK, write.pointsWrittenOK/subWriteDrop/valuesWrittenOK, hh_database

Follow-up to #7557.

##### Relevant URLs
- content/shared/influxdb-v1/administration/monitor/measurements-internal.md

## What

`content/shared/influxdb-v1/administration/monitor/measurements-internal.md`
documents four `_internal` fields and one Enterprise-only measurement that
are absent on two live InfluxDB v1.12.4 instances (OSS and Enterprise),
tested after fresh write and query activity:

- `httpd.valuesWrittenOK`
- `write.pointsWrittenOK`
- `write.subWriteDrop`
- `write.valuesWrittenOK`
- `hh_database` (measurement)

The four fields are still documented by the Telegraf `influxdb` input
plugin README (`content/telegraf/v1/input-plugins/influxdb.md`), so they
may exist only in older InfluxDB 1.x releases rather than being incorrect.
`hh_database` requires an active hinted handoff failure between cluster
nodes to reproduce, which wasn't testable with the available single-node
Enterprise setup.

A `` comment marks the spot in the doc.

## Ask

- Confirm whether the four fields exist in any currently supported
InfluxDB 1.x release, and if so, which version(s).
- Confirm whether `hh_database` is still emitted by InfluxDB Enterprise
during hinted handoff, and under what conditions.

## Definition of done

- [ ] Fields/measurement confirmed to exist (with version) → uncomment and
document properly, noting the version floor
- [ ] Fields/measurement confirmed removed/never existed → delete from the
doc and drop this note