[ft] Remove TODO item re FT_LOAD_IGNORE_GLOBAL_ADVANCE_WIDTH

That flag is redundant, deprecated, and ignored since April 2011.
From FreeType git log:

commit 8c82ec5b17d0cfc9b0876a2d848acc207a62a25a
Author: Behdad Esfahbod <behdad@behdad.org>
Date:   Thu Apr 21 08:21:37 2011 +0200

    Always ignore global advance.

    This makes FT_LOAD_IGNORE_GLOBAL_ADVANCE_WIDTH redundant,
    deprecated, and ignored.  The new behavior is what every major user
    of FreeType has been requesting.  Global advance is broken in many
    CJK fonts.  Just ignoring it by default makes most sense.

    * src/truetype/ttdriver.c (tt_get_advances),
    src/truetype/ttgload.c (TT_Get_HMetrics, TT_Get_VMetrics,
    tt_get_metrics, compute_glyph_metrics, TT_Load_Glyph),
    src/truetype/ttgload.h: Implement it.

    * docs/CHANGES: Updated.

src/hb-ft.cc

@@ -60,8 +60,6 @@
  *   - I believe transforms are not correctly implemented.  FreeType does not
  *     provide any API to get to the transform/delta set on the face. :(
  *
- *   - Always use FT_LOAD_IGNORE_GLOBAL_ADVANCE_WIDTH?
- *
  *   - FT_Load_Glyph() is exteremely costly.  Do something about it?
  */