Remove ash dependencies from exo when not using ChromeOS

Removed ash dependencies within EXO BUILD.gn file to allow
non-ChromeOS compilation.

Bug: 896710
Test: Compiled client on ChromeOS and verified it still builds.
Change-Id: I57b36c10ad55a609b7969f00b225abecd2f55fd9
Reviewed-on: https://chromium-review.googlesource.com/c/1288894
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Shawn Gallea <sagallea@google.com>
Cr-Commit-Position: refs/heads/master@{#601204}
1 file changed