remove strikeToSourceRatio from SkStrikeSpec

Change-Id: Ic8b9753f87ec3170a5dc98c19020929ea805797c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/469058
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Herb Derby <herb@google.com>
6 files changed