delete TabletHealth from healthy during deleteTablet

[xhh1989]

I have a question why not delete TabletHealth from healthy druing deleteTablet.
https://github.com/vitessio/vitess/blob/master/go/vt/discovery/healthcheck.go#L376
for example, an app can read from any replica, we call GetHealthyTabletStats(ks, shard, replica) read from replica, we did some changes in vitess, if GetHealthyTabletStats(ks, shard, replica) returned an empty list, we will call GetHealthyTabletStats(ks, shard, rdonly) instead , but now GetHealthyTabletStats(ks, shard, replica) may return an replica list with unhealthy replicas, that cause an error to app, besides according to the function name, it should not return an unhealthy replica.
It maybe better to delete TabletHealth from healthy during deleteTablet called.