[Extensions] Update DownloadTests to manifest v2

DownloadTests have been updated to manifest v2.
Remove the allowance for manifest v1 extensions.

Bug: 816679
Change-Id: If536e7da72deb5934305bf0a68b011b6b55582d5
Reviewed-on: https://chromium-review.googlesource.com/1026070Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553616}

chrome/browser/download/download_browsertest.cc

@@ -112,7 +112,6 @@
 #include "extensions/browser/extension_dialog_auto_confirm.h"
 #include "extensions/browser/extension_system.h"
 #include "extensions/browser/scoped_ignore_content_verifier_for_test.h"
-#include "extensions/common/switches.h"
 #include "net/base/filename_util.h"
 #include "net/dns/mock_host_resolver.h"
 #include "net/test/embedded_test_server/embedded_test_server.h"
@@ -452,14 +451,6 @@ class DownloadTest : public InProcessBrowserTest {
 
   DownloadTest() {}
 
-  void SetUpCommandLine(base::CommandLine* command_line) override {
-    InProcessBrowserTest::SetUpCommandLine(command_line);
-
-    // TODO(devlin): Remove this. See https://crbug.com/816679.
-    command_line->AppendSwitch(
-        extensions::switches::kAllowLegacyExtensionManifests);
-  }
-
   void SetUpOnMainThread() override {
     BrowserThread::PostTask(
         BrowserThread::IO, FROM_HERE,