Revert of Fix colorType/alphaType checks in SkCodec (patchset #5 id:80001 of https...

Revert of Fix colorType/alphaType checks in SkCodec (patchset #5 id:80001 of https://codereview.chromium.org/1695473002/ )

Reason for revert:
Really bad images in Gold.

Original issue's description:
> Fix colorType/alphaType checks in SkCodec
>
> Make getPixels() and startScanlineDecode() behave
> consistently.
>
> Require that kGray8 decodes are opaque.
>
> Assert that creating the swizzler succeeds.
>
> BUG=skia:4203
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1695473002
>
> Committed: https://skia.googlesource.com/skia/+/c7578b6cdd03b61f076ffc7956efd952d6c301c0

TBR=scroggo@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:4203

Review URL: https://codereview.chromium.org/1694023002