Remove refTypefaceOrDefault and getTypefaceOrDefault from SkFont API

The concept of a default Typeface will be going away as the concept
of a default FontMgr does.

A future CL will change a default Typeface to return null
and then this API can go away.

Client CLs:
 - http://cl/573930788
 - https://github.com/flutter/engine/pull/46969

Change-Id: Ibe6b06443cabd176382fa7bbfb48b89ffcdd7749
Bug: b/305780908
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/766776
Reviewed-by: Ben Wagner <bungeman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
25 files changed