[glyf] remove_hinting should del program from composite glyph

Unlike simple glyphs, which always have 'program' attribute (even when empty, with no instructions)
in composite glyphs, it's the presence of 'program' attribute that determines whether
the optional WE_HAVE_INSTRUCTIONS component flag is set or not.
Thus, the trim method (with remove_hinting=True) should delete the attribute for
composite glyphs.

Fixes https://github.com/fonttools/fonttools/issues/1550
2 files changed