Remove ProxyResolver from update_engine

Current ProxyResolver code only supports no-proxy. Therefore it is
barely any use. Remove current implementation for a better one.

Test: th
Bug: 235816007
Change-Id: Ieb46dedf6c6ea86b11c81d7691c2adb578d3d97d
diff --git a/libcurl_http_fetcher.h b/libcurl_http_fetcher.h
index 4e91b69..c101d90 100644
--- a/libcurl_http_fetcher.h
+++ b/libcurl_http_fetcher.h
@@ -82,8 +82,7 @@
 
 class LibcurlHttpFetcher : public HttpFetcher {
  public:
-  LibcurlHttpFetcher(ProxyResolver* proxy_resolver,
-                     HardwareInterface* hardware);
+  LibcurlHttpFetcher(HardwareInterface* hardware);
 
   // Cleans up all internal state. Does not notify delegate
   ~LibcurlHttpFetcher() override;
@@ -165,10 +164,6 @@
   // closing a socket created with the CURLOPT_OPENSOCKETFUNCTION callback.
   static int LibcurlCloseSocketCallback(void* clientp, curl_socket_t item);
 
-  // Callback for when proxy resolution has completed. This begins the
-  // transfer.
-  void ProxiesResolved();
-
   // Asks libcurl for the http response code and stores it in the object.
   virtual void GetHttpResponseCode();