Update orgmode glyph

[why]
The glyph is needlessly detailed (for a font).
There is another, more simple glyph, which is also used by fileicons.

More details see PR #833.

Reported-by: tecosaur <contact@tecosaur.net>
Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>