Revert "[skif] Add transparent padding to source saveLayers"

This reverts commit 74661f1ccf74f7d1d243ccfff505f5355774b998.

Reason for revert: breaking Flutter roll

Original change's description:
> [skif] Add transparent padding to source saveLayers
>
> Bug: b/323886195
> Change-Id: I29bcdf6832ebe53f816764438b3d0017909bdafd
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/813016
> Commit-Queue: Michael Ludwig <michaelludwig@google.com>
> Reviewed-by: Brian Osman <brianosman@google.com>

Bug: b/323886195
Change-Id: Iae3e5bb6fdf4d8fb8bf710384c9152f77da3275d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/818976
Auto-Submit: John Stiles <johnstiles@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
5 files changed