Port engine_1_20_0.py over to use SafeUpload, delete 1.17 recipes.

When I initially landed my SafeUpload change (https://flutter-review.googlesource.com/c/recipes/+/5040), I only applied it to the latest engine recipe, so as to not interfere with the Stable release (`1.20`). Now apply it to the `1.20` recipe. Also, delete 1.17 recipes, as they are no longer used.

Change-Id: I75b3deaa8282cbfd0cae8aab2b8d46b11915f255
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/5360
Reviewed-by: Godofredo Contreras <godofredoc@google.com>
Commit-Queue: Christopher Fujino <fujino@google.com>
108 files changed
tree: 536167b7b3a4813fc2d14359980a0c1dae0c9076
  1. infra/
  2. recipe_modules/
  3. recipes/
  4. .gitignore
  5. .style.yapf
  6. OWNERS
  7. recipes.py