Make the skia-wasm-release image only have the build products

The previous version had several gigs of buildtools, source code, etc.
This is much smaller and easier to download for tools like
jsfiddles.skia.org and (soon) skottie.skia.org

Bug: skia:
Change-Id: I748487abb1c6f6e82476076d22a27a5d4f90f75a
Reviewed-on: https://skia-review.googlesource.com/c/169240
Reviewed-by: Kevin Lubick <kjlubick@google.com>
1 file changed