[API] Remove const from font user_data
diff --git a/src/hb-ft.cc b/src/hb-ft.cc
index 3fe2365..a0c7521 100644
--- a/src/hb-ft.cc
+++ b/src/hb-ft.cc
@@ -38,12 +38,12 @@
 
 static hb_bool_t
 hb_ft_get_contour_point (hb_font_t *font HB_UNUSED,
-			 const void *font_data,
+			 void *font_data,
 			 hb_codepoint_t glyph,
 			 unsigned int point_index,
 			 hb_position_t *x,
 			 hb_position_t *y,
-			 const void *user_data HB_UNUSED)
+			 void *user_data HB_UNUSED)
 {
   FT_Face ft_face = (FT_Face) font_data;
   int load_flags = FT_LOAD_DEFAULT;
@@ -67,11 +67,11 @@
 
 static void
 hb_ft_get_glyph_advance (hb_font_t *font HB_UNUSED,
-			 const void *font_data,
+			 void *font_data,
 			 hb_codepoint_t glyph,
 			 hb_position_t *x_advance,
 			 hb_position_t *y_advance,
-			 const void *user_data HB_UNUSED)
+			 void *user_data HB_UNUSED)
 {
   FT_Face ft_face = (FT_Face) font_data;
   int load_flags = FT_LOAD_DEFAULT;
@@ -87,10 +87,10 @@
 
 static void
 hb_ft_get_glyph_extents (hb_font_t *font HB_UNUSED,
-			 const void *font_data,
+			 void *font_data,
 			 hb_codepoint_t glyph,
 			 hb_glyph_extents_t *extents,
-			 const void *user_data HB_UNUSED)
+			 void *user_data HB_UNUSED)
 {
   FT_Face ft_face = (FT_Face) font_data;
   int load_flags = FT_LOAD_DEFAULT;
@@ -109,10 +109,10 @@
 
 static hb_codepoint_t
 hb_ft_get_glyph (hb_font_t *font HB_UNUSED,
-		 const void *font_data,
+		 void *font_data,
 		 hb_codepoint_t unicode,
 		 hb_codepoint_t variation_selector,
-		 const void *user_data HB_UNUSED)
+		 void *user_data HB_UNUSED)
 
 {
   FT_Face ft_face = (FT_Face) font_data;
@@ -130,12 +130,12 @@
 
 static void
 hb_ft_get_kerning (hb_font_t *font HB_UNUSED,
-		   const void *font_data,
+		   void *font_data,
 		   hb_codepoint_t first_glyph,
 		   hb_codepoint_t second_glyph,
 		   hb_position_t *x_kern,
 		   hb_position_t *y_kern,
-		   const void *user_data HB_UNUSED)
+		   void *user_data HB_UNUSED)
 {
   FT_Face ft_face = (FT_Face) font_data;
   FT_Vector kerning;