Stop generating separate rust_test_host.

With b/196306316 hopefully fixed, we should be able to use a single
rust_test entry for both device and host tests.  This modifies
cargo2android.py so it generates these shared tests.

Test: Run on crates with simple tests, those with defaults, host-only,
and device-only tests.

Change-Id: Icfe8d1fb26a61bc9ed65b8a7b116a4ebcd782ce4
2 files changed