Replace U+01B5 with U+017B in Polish teletext

Both U+01B5 and U+017B refer to the same character, but
with a little different look. U+01B5 is used with teletext
pages only, while U+017B is used with subtitles.
U+01B5 is not implemented in any ttf file, while
tuxtxt.otb has both charaters defined with U+01B5 look.