Issue #2191 - Remove as much old fontconfig support as needed for Harfbuzz update.

Based on Mozilla bugs 1119128, 1285533, and 1421964.

gfx.font_rendering.fontconfig.fontlist.enabled is no longer available.

gfxFontconfigUtils.h still exists, and will be removed in another commit. Just
need more research on bug 1385029.

Tag #1862

gfx/thebes/gfxPlatformGtk.h

@@ -111,8 +111,6 @@ public:
     }
 #endif
 
-    static bool UseFcFontList() { return sUseFcFontList; }
-
     bool UseImageOffscreenSurfaces();
 
     virtual gfxImageFormat GetOffscreenFormat() override;
@@ -154,10 +152,6 @@ private:
 #ifdef MOZ_X11
     Display* mCompositorDisplay;
 #endif
-
-    // xxx - this will be removed once the new fontconfig platform font list
-    // replaces gfxPangoFontGroup
-    static bool sUseFcFontList;
 };
 
 #endif /* GFX_PLATFORM_GTK_H */