Clean up SkFontConfigInterface implementation.

src/ports/SkFontConfigInterface_direct.h

 /*
  * Copyright 2009-2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /* migrated from chrome/src/skia/ext/SkFontHost_fontconfig_direct.cpp */
 
 #include "SkFontConfigInterface.h"
-#include "SkMutex.h"
 
 #include <fontconfig/fontconfig.h>
 
 class SkFontConfigInterfaceDirect : public SkFontConfigInterface {
 public:
     SkFontConfigInterfaceDirect();
     ~SkFontConfigInterfaceDirect() override;
 
     bool matchFamilyName(const char familyName[],
                          SkFontStyle requested,
                          FontIdentity* outFontIdentifier,
                          SkString* outFamilyName,
                          SkFontStyle* outStyle) override;
 
     SkStreamAsset* openStream(const FontIdentity&) override;
 
     // new APIs
     SkDataTable* getFamilyNames() override;
 
 protected:
     virtual bool isAccessible(const char* filename);
 
 private:
-    SkMutex mutex_;
-
     bool isValidPattern(FcPattern* pattern);
     FcPattern* MatchFont(FcFontSet* font_set, const char* post_config_family,
                          const SkString& family);
     typedef SkFontConfigInterface INHERITED;
 };