Summary: Since 066032b6e6 was merged, the `nix flake check` build no longer
overrides the 'cargo test' profile explicitly, to save disk space. The CI seems
to be in a better spot. This will stem the tide for a while hopefully.
However, with that change in place, the `nix flake check` build was
essentially a redundant, nearly-identical copy of a normal `nix build` with no
differentiating features, except: `RUST_BACKTRACE` is set to 1.
Delete all this code, and remove it from the CI matrix, and instead just export
`RUST_BACKTRACE` on the `checkPhase` of the normal `nix build` instead, which is
functionally equivalent.
Also does some minor, no-functional-change touchups to `flake.nix` while I was
there (whitespace, etc.)
Signed-off-by: Austin Seipp <aseipp@pobox.com>
Change-Id: I87336b16e2a0b973343ecbde8ffd7b8f
71a3045032