build_emoji: Remove now unused `color_font()` function.

This function was used to color transparent number emojis. We no
longer need to do this since now we have remapped number emojis
to the corresponding colored emojis in the new emoji farm.

tools/setup/emoji/build_emoji

@@ -93,33 +93,6 @@ if 'TRAVIS' in os.environ:
 class MissingGlyphError(Exception):
     pass
 
-def color_font(name, code_point, code_point_to_fname_map):
-    # type: (str, str, Dict[int, Union[Text, bytes]]) -> None
-    glyph_name = code_point_to_fname_map[int(code_point, 16)]
-
-    in_name = 'bitmaps/strike0/{}.png'.format(glyph_name)
-    out_name = 'out/unicode/{}.png'.format(code_point)
-
-    # These emojis are colored white and need to be recolored
-    white_emojis = ['eight', 'five', 'four', 'hash', 'nine', 'one',
-                    'seven', 'six', 'three', 'two', 'zero']
-
-    try:
-        if name in white_emojis:
-            white_emoji_image = Image.open(in_name).convert('RGBA')
-            # Reduced image size for having a 4-pixel dark yellow background
-            # on right and bottom of the image.
-            light_yellow_background = Image.new('RGBA', (124, 124), '#FCC21B')
-            dark_yellow_background = Image.new('RGBA', SIZE, '#F79329')
-            # Paste the image on a light yellow background and the resulting
-            # image on a dark yellow background.
-            light_yellow_background.paste(white_emoji_image, mask=white_emoji_image)
-            dark_yellow_background.paste(light_yellow_background, mask=light_yellow_background)
-            dark_yellow_background.save(in_name)
-        shutil.copyfile(in_name, out_name)
-    except IOError:
-        raise MissingGlyphError('code_point: %r' % (code_point))
-
 
 def bw_font(name, code_point):
     # type: (str, str) -> None