remove unused code

Summary:
remove unused code

this is logged as part of the

```
        if let Some(client_info) = metadata.client_request_info() {
            scuba.add_client_request_info(client_info);
        }
```

Reviewed By: lmvasquezg

Differential Revision: D72171667

fbshipit-source-id: 479b71d3f3445f3e85186813cb41f7b74d1f322e

Author: Liubov Dmitrieva

eden/mononoke/gotham_ext/src/middleware/scuba.rs

@@ -69,8 +69,6 @@ pub enum HttpScubaKey {
     ResponseContentEncoding,
     /// The IP of the connecting client.
     ClientIp,
-    /// The client correlator submitted by the client, if any.
-    ClientCorrelator,
     /// The client identities received for the client, if any.
     ClientIdentities,
     /// Alias of the sandcastle job, if any.
@@ -122,7 +120,6 @@ impl AsRef<str> for HttpScubaKey {
             ResponseContentLength => "response_content_length",
             ResponseContentEncoding => "response_content_encoding",
             ClientIp => "client_ip",
-            ClientCorrelator => "client_correlator",
             ClientIdentities => "client_identities",
             SandcastleAlias => "sandcastle_alias",
             SandcastleVCS => "sandcastle_vcs",