Remove libcurl support from update_engine_sideload.

While sideloading an update from recovery we don't need nor want to
download payload from HTTP(S) URLs, only local file:// are supported.
This patch moves libcurl_http_fetcher and certificate_checker files out
of libpayload_consumer dropping the libcurl and libssl dependencies from
it and the update_engine_sideload.

Bug: 27178350
TEST=build UE for Brillo and Android. Unittests still pass and
update_engine_sideload doesn't link to libcurl.

Change-Id: Iffefdb094654f7277dc825c041fe55aac9ee8756
diff --git a/update_attempter_android.cc b/update_attempter_android.cc
index 61d2828..2de2667 100644
--- a/update_attempter_android.cc
+++ b/update_attempter_android.cc
@@ -29,7 +29,6 @@
 
 #include "update_engine/common/constants.h"
 #include "update_engine/common/file_fetcher.h"
-#include "update_engine/common/libcurl_http_fetcher.h"
 #include "update_engine/common/multi_range_http_fetcher.h"
 #include "update_engine/common/utils.h"
 #include "update_engine/daemon_state_interface.h"
@@ -39,6 +38,12 @@
 #include "update_engine/payload_consumer/postinstall_runner_action.h"
 #include "update_engine/update_status_utils.h"
 
+#ifndef _UE_SIDELOAD
+// Do not include support for external HTTP(s) urls when building
+// update_engine_sideload.
+#include "update_engine/libcurl_http_fetcher.h"
+#endif
+
 using base::Bind;
 using base::TimeDelta;
 using base::TimeTicks;
@@ -435,10 +440,14 @@
     DLOG(INFO) << "Using FileFetcher for file URL.";
     download_fetcher = new FileFetcher();
   } else {
+#ifdef _UE_SIDELOAD
+    LOG(FATAL) << "Unsupported sideload URI: " << url;
+#else
     LibcurlHttpFetcher* libcurl_fetcher =
         new LibcurlHttpFetcher(&proxy_resolver_, hardware_);
     libcurl_fetcher->set_server_to_check(ServerToCheck::kDownload);
     download_fetcher = libcurl_fetcher;
+#endif  // _UE_SIDELOAD
   }
   shared_ptr<DownloadAction> download_action(new DownloadAction(
       prefs_,