Also update SampleApplication to request the default
renderer instead of explicitely asking for d3d11

BUG=angleproject:892

Change-Id: I70c431b3c1ba78c3ce7844d7f276cc19ac17d7f5
Reviewed-on: https://chromium-review.googlesource.com/269999Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>