[gold] Clean image for ingestion
[gold] Clean image for ingestion

Change-Id: Ibc67f9c25d07968ed3c66fc0a88a245cef99d8b4
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/378966
Reviewed-by: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot