[ft] Disable ppem setting

The calculations were wrong.

FreeType makes it really hard to set size and ppem independently.
For now, disable it.  Need to come up with a fix later.
diff --git a/src/hb-ft.cc b/src/hb-ft.cc
index 17c68df..90937ca 100644
--- a/src/hb-ft.cc
+++ b/src/hb-ft.cc
@@ -466,8 +466,11 @@
 
   FT_Set_Char_Size (ft_face,
 		    font->x_scale, font->y_scale,
+		    0, 0);
+#if 0
 		    font->x_ppem * 72 * 64 / font->x_scale,
 		    font->y_ppem * 72 * 64 / font->y_scale);
+#endif
 
   ft_face->generic.data = blob;
   ft_face->generic.finalizer = (FT_Generic_Finalizer) _release_blob;