Fix drop measurement not dropping all data

If there were multiple shards, drop measurement could update the index
and remove the measurement before the other shards ran their deletes.
This causes the later shards to not see any series to delete.

The fix is to all deleteSeries to handle the index delete which already
accounts for removing the measurement when it is fully removed from the
index.

tsdb/engine/tsm1/engine.go

@@ -1046,11 +1046,6 @@ func (e *Engine) deleteMeasurement(name []byte) error {
 			return err
 		}
 	}
-
-	// Remove the measurement from the index.
-	if err := e.index.DropMeasurement(name); err != nil {
-		return err
-	}
 	return nil
 }