Roll Vulkan-ValidationLayers from f074521d88d4 to 6668e1afddc9 (2 revisions)

https://chromium.googlesource.com/external/github.com/KhronosGroup/Vulkan-ValidationLayers/+log/f074521d88d4..6668e1afddc9

2021-02-02 s.fricke@samsung.com tests: Fix various tests failing on MockICD
2021-02-02 s.fricke@samsung.com tests: Add VK_DEVSIM_MODIFY_EXTENSION_LIST to docs

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https://autoroll.skia.org/r/vulkan-validation-layers-vulkan-deps
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Tbr: angle-bots+autoroll-info@google.com
Change-Id: I0898a29c540c778d16136855a55cea5cd6eb0a11
Reviewed-on: https://chromium-review.googlesource.com/c/vulkan-deps/+/2666255
Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>

• DEPS[diff]