Revert "Vectorize scalars in SPIR-V using ConstructorSplat."

This reverts commit 5d61cc2f87a9f988e68497be850a20926e473d04.

Reason for revert: break Vk bots

Original change's description:
> Vectorize scalars in SPIR-V using ConstructorSplat.
>
> This avoids redundant code, and has a small side benefit of
> deduplicating constant vectors which appear more than once in the code,
> since `writeConstructorSplat` already supports this.
>
> Change-Id: I2972ee922ac92adeb40bc765da3b490a59b957b3
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/408360
> Auto-Submit: John Stiles <johnstiles@google.com>
> Reviewed-by: Brian Osman <brianosman@google.com>
> Commit-Queue: John Stiles <johnstiles@google.com>

TBR=brianosman@google.com,ethannicholas@google.com,johnstiles@google.com

Change-Id: I9fc0b896c0cfccc348d510a02df47d5ad74a0e90
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/408644
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
12 files changed