This extension was never actually implemented. While it has been
promoted to 'core' in Vulkan 1.1, the storageBuffer16BitAccess feature
bit indicates whether or not the implementation supports the
functionality.

Bug: b/162742397
Test: dEQP-VK.info.device_mandatory_features
Change-Id: I3e2871ce09975db3da2ad1f042d6955dbd565479
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/47408
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Sean Risser <srisser@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>