Fix Dockerfile so args.gn actually applies, also drop debug symbols.

The part of the Dockerfile that extracted the skiaserve executable
will be done in the skiabot repo.

Bug: skia:
Change-Id: Ieb913908d92626a7b9e68649b5c56b8f92646fd2
Reviewed-on: https://skia-review.googlesource.com/130323
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
3 files changed