This reverts commit 0ad1559f.

Reason for revert: linux-rel no-op build issue showing up in Chromium integration. Tracking in chromium:997016

Original change's description:
> Reland "Vulkan: Use VK repos' internal BUILD.gn files"
> 
> This is a reland of 552f5fcb
> 
> Original change's description:
> > Vulkan: Use VK repos' internal BUILD.gn files
> >
> > This retires custom BUILD.gn files for the Vulkan Headers, Tools,
> > Validation-Layers, and Loader repos. They now have integrated BUILD.gn
> > files so switched ANGLE to use those by default.
> > Also Validation Layer, Loader, and Tools repos no longer uses codegen
> > so this speeds up the build overall.
> > Switched over from old VK_LAYER_LUNARG_standard_validation meta-layer
> > to VK_LAYER_KHRONOS_validation unified layer.
> >
> > This changes includes a temporary workaround to the Vulkan-Loader repo
> > to remove its Window's build dependence on WDK. There are plans to
> > remove that depenedence in Loader master, but until then we can use
> > our custom branch workaround.
> > It also includes a custom branch for validation layers that includes
> > some build fixes for ANGLE.
> > Finally, the layers were crashing on Android when attempting to use
> > DebugUtils extension so forcing DebugReport on Android for now.
> >
> > Bug: angleproject:2449
> > Bug: angleproject:3320
> > Bug: angleproject:3852
> > Bug: chromium:997009
> > Bug: chromium:997016
> > Change-Id: I48b36acefcc7f2bc930eb72d6fdbc87bca24f833
> > Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1610438
> > Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
> > Reviewed-by: Jamie Madill <jmadill@chromium.org>
> > Commit-Queue: Tobin Ehlis <tobine@google.com>
> 
> Bug: angleproject:2449, angleproject:3320, angleproject:3852
> Change-Id: I9597be99000083b135e19b6ee68d4ae222158e72
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1769036
> Commit-Queue: Tobin Ehlis <tobine@google.com>
> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>

TBR=tobine@google.com,syoussefi@chromium.org,jmadill@chromium.org

Change-Id: I88afdaff07e9f414f9de02f6d3651eaba9a5045f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:2449, angleproject:3320, angleproject:3852
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1776920Reviewed-by: Tobin Ehlis <tobine@google.com>
Commit-Queue: Tobin Ehlis <tobine@google.com>