Clean up cros-rust ebuilds in dev-rust and sys-apps.

This enables unit testing on arm and aarch64. The minijail ebuilds will
be handled in a follow up CL.

BUG=chromium:1158447
TEST=CQ passes

Change-Id: Ifa8d8bf6b17c4af7ffc47be3330b9c297da69ca1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2590490
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
Commit-Queue: Allen Webb <allenwebb@google.com>
Tested-by: Allen Webb <allenwebb@google.com>
4 files changed