Bug 1307216 - Remove warning about non-existent plug-in registry key. r=bsmedberg

It's possible the plugin key doesn't exist, there's no need to warn about that.

MozReview-Commit-ID: Law8J9zUHCt

--HG--
extra : rebase_source : d80ac46094c55281490659d622a4cdd8c2a95c86

dom/plugins/base/nsPluginHost.cpp

@@ -2359,7 +2359,7 @@ WatchRegKey(uint32_t aRoot, nsCOMPtr<nsIWindowsRegKey>& aKey)
   nsresult rv = aKey->Open(aRoot,
                            NS_LITERAL_STRING("Software\\MozillaPlugins"),
                            nsIWindowsRegKey::ACCESS_READ | nsIWindowsRegKey::ACCESS_NOTIFY);
-  if (NS_WARN_IF(NS_FAILED(rv))) {
+  if (NS_FAILED(rv)) {
     aKey = nullptr;
     return;
   }