The GN build gets many default flags from //build/config. Remove
flags that are redundant with the default flags.
No intended behavior change (except for the hash style).
Bug: chromium:1220175
Change-Id: Idcebc8f55165ae300632005f5cf527ec689a365f
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/55608Reviewed-by: Alexis Hétu <sugoi@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
