chromeos-base: Cleanup cros-rust ebuilds.

This enables unit testing on arm and aarch64.

BUG=chromium:1158447
TEST=CQ passes

Change-Id: Idb63ac6548d7de79b200c9e003cf832067c03518
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2590484
Tested-by: Allen Webb <allenwebb@google.com>
Auto-Submit: Allen Webb <allenwebb@google.com>
Commit-Queue: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
5 files changed