Remove a superfluous qualifier on an inline method.

Fixes
..\..\third_party\webrtc/base/stringutils.h(295,49) :  warning(clang): extra qualification on member "empty_str" [-Wmicrosoft]

No behavior change, but makes the code more standards-conformant.

BUG=chromium:505296

Review URL: https://codereview.webrtc.org/1228193002

Cr-Commit-Position: refs/heads/master@{#9562}
diff --git a/webrtc/base/stringutils.h b/webrtc/base/stringutils.h
index 25990e0..5a6f42a 100644
--- a/webrtc/base/stringutils.h
+++ b/webrtc/base/stringutils.h
@@ -292,7 +292,7 @@
 template<>
 struct Traits<wchar_t> {
   typedef std::wstring string;
-  inline static const wchar_t* Traits<wchar_t>::empty_str() { return L""; }
+  inline static const wchar_t* empty_str() { return L""; }
 };
 
 #endif  // WEBRTC_WIN