[raszi]

Update the dependencies and remove the dead code.

• Update all dependencies: git2 0.21, cucumber 0.23, shlex 2, and the compatible versions.
• Remove pkg-config, openssl, and zlib from devenv.nix, because git2 no longer needs them.
• Remove the unused Display and the commented-out dependencies.
• Reject an invalid glob with a clap error instead of a panic.
• Fail the tests on a skipped step, so a typo in a feature file cannot turn off a test.