This reverts commit 1224802c.

Reason for revert: https://bugs.chromium.org/p/angleproject/issues/detail?id=3912

Original change's description:
> Vulkan: SwiftShader integration.
> 
> Adds a new EGL extension for picking SwiftShader when using the Vulkan
> back-end. Also cleans up ICD enabling code RendererVk. Also includes a
> change to a buffer size necessary to support SwiftShader's minimum
> limits.
> 
> 32-bit is currently left disabled to work around an issue on AMD Win7.
> 
> Bug: angleproject:3876
> Bug: b/140251624
> Change-Id: I33c55d994801d6154caca0cad0a608c1e808d517
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1776231
> Commit-Queue: Jamie Madill <jmadill@chromium.org>
> Reviewed-by: Geoff Lang <geofflang@chromium.org>

TBR=geofflang@chromium.org,jonahr@google.com,jmadill@chromium.org

Change-Id: Id7464250f6941b0228a6b2a9bd0349823727275b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:3876, b/140251624
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1808101Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: Zhenyao Mo <zmo@chromium.org>