It turns out that "cargo test --release" doesn't use
`[profile.release]`; it uses `[profile.bench]` instead; see
[here](https://doc.rust-lang.org/cargo/reference/manifest.html) for details.
So the plan to run the tests in optimized mode but with debug-assertions
enabled didn't actually work, and we had an actual failing unit test that
was hidden because assertions were disabled.
So, this makes test-all.sh just run the unit tests in debug mode, as is
the norm for Rust packages, and fixes the buggy test.
This also removes the `[profile.release]` override from the top-level
Cargo.toml file too. We don't need it now that we're not running tests
in release mode, and it had confused multiple people because it made
Cretonne's in-tree builds different from how Cretonne is built when used as
a dependency in other projects.
07576d3ed0