Remove useless wxFont::ActivatePrivateFonts()

Just "activate" the font immediately when adding it using
AddPrivateFont(), nothing seems to be gained from having two functions
and it just makes things more complicated both when implementing and
when using the API.

include/wx/font.h

@@ -328,11 +328,12 @@ public:
     // from the string representation of wxNativeFontInfo
     static wxFont *New(const wxString& strNativeFontDesc);
 
-    // These functions can be used to load private fonts if supported by this
-    // platform (wxHAS_PRIVATE_FONTS is defined): first add one or more files
-    // and then activate all of them at once.
+    // Load the font from the given file and return true on success or false on
+    // error (an error message will be logged in this case, unless there is no
+    // support for private fonts at all in the current port, in which case
+    // wxHAS_PRIVATE_FONTS will not be defined allowing to check for this at
+    // compile-time).
     static bool AddPrivateFont(const wxString& filename);
-    static bool ActivatePrivateFonts();
 
     // comparison
     bool operator==(const wxFont& font) const;