clean up debug diagnostics in SkTestFont

We're going to be using this more often to the point that the extra
SkDebugf() calls are going to be annoying.

May also fix a crash?

Change-Id: I796037568cce720ecb3d0b4f4272af5d700760ea
Reviewed-on: https://skia-review.googlesource.com/70180
Reviewed-by: Ben Wagner <bungeman@google.com>
3 files changed