Reason for revert:
Precautionary revert for chromium:586487
Original issue's description:
> SkNx refactoring
>
> - add back Sk4i typedef
> - define SSE casts in terms of Sk4i
> * uint8 <-> float becomes uint8 <-> int <-> float
> * uint16 <-> float becomes uint16 <-> int <-> float
>
> This has the nice side effect of specializing uint8 <-> int
> and uint16 <-> int, which are useful in their own right.
>
> There are many cast specializations now, some of which call each other.
> I have tried to arrange them in some sort of sensible order, subject to
> the constraint that those called must precede those who call.
>
> BUG=skia:
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1690633003
> CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot
>
> Committed: https://skia.googlesource.com/skia/+/c1eb311f4e98934476f1b2ad5d6de772cf140d60TBR=herb@google.com,mtklein@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=chromium:586487
Review URL: https://codereview.chromium.org/1696903002
97120a7ed1