SwiftShader is not needed on Fuchsia because the platform is expected to
provide Vulkan on all devices.

Bug: fuchsia:37278
Change-Id: I96d49f51dbe473bd032ec966137f35d2df9b6884
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1822863Reviewed-by: Michael Spang <spang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>