[infra] Cleanup unused OS mappings in gen_tasks.go

Change-Id: I739f1e8cd0eda473dc1ea1fb822ddeed15ca8ba6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/202715
Commit-Queue: Eric Boren <borenet@google.com>
Auto-Submit: Ben Wagner <benjaminwagner@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
1 file changed