ref(consumers): Remove ErrorsProcessor (#6711)

This processor has been implemented in
rust_snuba/src/processors/errors.rs for quite a while now, and deployed
in US region since then. The python one should no longer be needed.

* Fix a user-facing bug where HTTP referers were no longer searchable,
as the `http_referer` column would always hold an empty string. The new
behavior is that any HTTP header like `Referer` or `Referrer` would be
used.
* Apparently the rust processor uses different hyphenization in
`contexts[trace_id]` than the python one. nobody noticed this as we use
a top-level trace_id column.

rust_snuba/src/processors/errors.rs

@@ -445,7 +445,7 @@ impl ErrorRow {
             .into_iter()
             .flatten()
         {
-            if key == "Referrer" {
+            if key == "Referer" || key == "Referrer" {
                 http_referer = value.0;
                 break;
             }