Upstream: removed compatibility shims from ngx_http_upstream_t.

The type is no longer modified in NGINX Plus.
diff --git a/src/http/ngx_http_upstream.h b/src/http/ngx_http_upstream.h
index 7390f2e..448d071 100644
--- a/src/http/ngx_http_upstream.h
+++ b/src/http/ngx_http_upstream.h
@@ -390,9 +390,6 @@
     unsigned                         request_sent:1;
     unsigned                         request_body_sent:1;
     unsigned                         header_sent:1;
-
-    NGX_COMPAT_BEGIN(1)
-    NGX_COMPAT_END
 };