This reverts commit d46e2fb1.

Reason for revert: Broke Vulkan angle_end2end_tests.

Bug: angleproject:3954 

Original change's description:
> GN: Componentize vulkan back-end build.
> 
> This moves the build configuration into the Vulkan back-end dir.
> This should be a little easier to maintain as all Vulkan-related
> config is in one place.
> 
> Note that this should not interfere with Skia's build as they do
> not import the Vulkan back-end sources.
> 
> One additional possiblity that this enables is testing other
> compile-time permutations of the Vulkan back-end more easily. For
> example we could make a simple change to enable compile testing
> of the Vulkan back-end with custom command buffers disabled.
> 
> Also fixes a few errors affecting less tested configs.
> 
> Bug: angleproject:3943
> Change-Id: Iaf819936896e4f5d3e6415ed16ab0c940e46cdb6
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1829662
> Commit-Queue: Jamie Madill <jmadill@chromium.org>
> Reviewed-by: Tobin Ehlis <tobine@google.com>

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

Change-Id: I7cf3db4f6b7d8b779625ea2491172bb429b498a9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:3943
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1837233Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>