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_unittest.cc b/libcurl_http_fetcher_unittest.cc
index 3543870..a944f37 100644
--- a/libcurl_http_fetcher_unittest.cc
+++ b/libcurl_http_fetcher_unittest.cc
@@ -23,7 +23,6 @@
 #include <gtest/gtest.h>
 
 #include "update_engine/common/fake_hardware.h"
-#include "update_engine/common/mock_proxy_resolver.h"
 #include "update_engine/mock_libcurl_http_fetcher.h"
 
 using std::string;
@@ -44,7 +43,7 @@
 
   brillo::FakeMessageLoop loop_{nullptr};
   FakeHardware fake_hardware_;
-  MockLibcurlHttpFetcher libcurl_fetcher_{nullptr, &fake_hardware_};
+  MockLibcurlHttpFetcher libcurl_fetcher_{&fake_hardware_};
   UnresolvedHostStateMachine state_machine_;
 };