Solr: DELETEREPLICA does not return messages when target core server was gone.

[Takumi Yoshida]

Hi,

I noticed that DELETEREPLICA action does not return messages when the target 
core status was gone.
Does anybody know intent of this change? (or a bug?)

url :
http://xxx.xxx.xxx.xxx:8983/solr/admin/collections?action=DELETEREPLICA&collection=testtest&shard=shard1&replica=core_node3

Solr 5.5.4:
```
<response>
<lst name="responseHeader">
<int name="status">0</int>
<int name="QTime">65203</int>
</lst>
<lst name="failure">
<str name="yyy.yyy.yyy.yyy:8983_solr">
org.apache.solr.client.solrj.SolrServerException:IOException occured when 
talking to server at: http://yyy.yyy.yyy.yyy:8983/solr
</str>
</lst>
</response>
```

Solr 6.4.2:
```
<response>
<lst name="responseHeader">
<int name="status">0</int>
<int name="QTime">189</int>
</lst>
</response>
```

Thanks,
Takumi Yoshida