Revert of Return color shader instead of 2-color gradient when color count is 1 ...

Revert of Return color shader instead of 2-color gradient when color count is 1 (patchset #3 id:40001 of https://codereview.chromium.org/2259823005/ )

Reason for revert:
breaks 2-pt-conical, which can sometimes not draw anything

Original issue's description:
> Return color shader instead of 2-color gradient when color count is 1
>
> BUG=skia:
> GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2259823005
>
> Committed: https://skia.googlesource.com/skia/+/da082a5767d7edfd3abe74fc683392422565a606

TBR=fmenozzi@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review-Url: https://codereview.chromium.org/2257993002