[Extensions] Update ExtensionIconSourceTests to manifest v2

Update ExtensionIconSourceTests to manifest v2 and remove the allowance
for manifest v1 extensions.

Bug: 816679
Change-Id: I6fe638994b9ca34b03fc16debcfb547d75e967e1
Reviewed-on: https://chromium-review.googlesource.com/1018405Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552093}

chrome/browser/extensions/extension_icon_source_apitest.cc

@@ -16,14 +16,7 @@
 #include "net/dns/mock_host_resolver.h"
 #include "url/gurl.h"
 
-class ExtensionIconSourceTest : public ExtensionApiTest {
- protected:
-  void SetUpCommandLine(base::CommandLine* command_line) override {
-    ExtensionApiTest::SetUpCommandLine(command_line);
-    command_line->AppendSwitch(
-        extensions::switches::kAllowLegacyExtensionManifests);
-  }
-};
+using ExtensionIconSourceTest = ExtensionApiTest;
 
 // Times out on Mac and Win. http://crbug.com/238705
 #if defined(OS_WIN) || defined(OS_MACOSX)