remove platform_font_name()

It's used rarely and now that we're mostly using portable fonts,
it only serves to confuse.  Sans-serif doesn't seem to work anyway.

Simplify gm/typeface.cpp to just test the default typeface.

Change-Id: I091239ea91af9d9e01d3c76280636a6061b5fb5c
Reviewed-on: https://skia-review.googlesource.com/71261
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
5 files changed