doc: remove DOT_FONTNAME from doxygen.in
doc: remove DOT_FONTNAME from doxygen.in

This one is no longer provided and we don't care about the font anyway.

Signed-off-by: Peter Hutterer <b9c50af7afa7642f6f854434cda9ffe54ece8b85@who-t.net>

freedesktop-unofficial-mirror/xorg__test__xorg-gtest,freedesktop-unofficial-mirror/xorg__test__xorg-gtest,freedesktop-unofficial-mirror/xorg__test__xorg-gtest