HDR gainmaps: Require Version 1.0

Enough time has passed since we started writing Version 1.0 into the
files that it's now safe to break any files that didn't have this.

Bug: skia:14031
Change-Id: I74048a7f03c5cbdc3302574e5aa78a0ebd81e937
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/700196
Commit-Queue: ccameron chromium <ccameron@chromium.org>
Commit-Queue: Christopher Cameron <ccameron@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed