DROP SHARD doesn't remove data from _internal

[beckettsean]

Bug report

System info:
InfluxDB 0.13

Steps to reproduce:

> drop shard 257
> SELECT "writePointsOk",id  FROM "_internal".."shard" WHERE time > now() - 10s group BY *
name: shard
tags: clusterID=36934674580451795, database=_internal, engine=tsm1, hostname=sean-stable, id=252, nodeID=0, path=/var/lib/influxdb/data/_internal/monitor/252, retentionPolicy=monitor
time            writePointsOk   id
----            -------------   --
1468005095000000000 317511      252

<snip>

name: shard
tags: clusterID=36934674580451795, database=mydb, engine=tsm1, hostname=sean-stable, id=257, nodeID=0, path=/var/lib/influxdb/data/mydb/default/257, retentionPolicy=default
time            writePointsOk   id
----            -------------   --
1468005095000000000 1       257

<snip>
> 

(The shard only had one point before being dropped, so that's consistent output)

Expected behavior:

Once dropped, the shard should not appear in _internal monitoring. For shards removed by retention policy expiration things work as expected, but for manually dropped shards the data persists.

Actual behavior:

Statistics about shards that have been dropped by DROP SHARD persist in _internal

Additional info:

[beckettsean]

@rkuchan, nice catch

@jsternberg is in the midst of a PR that should resolve this.

[jsternberg]

This should be fixed with #6964. If this is still an issue with that fix, please reopen so I can take another look and address the problem.