This PR removes dead code.

What's interesting is that it has a bug in it, so it probably was never used :) The correct implementation would be:

  /// Gets the parsed command-line option named [name] as an `int`.
  int? intArg(String name) {
    if (!argParser.options.containsKey(name)) {
      return null;
    }

    final value = argResults![name] as String?;
    if (value == null) {
      return null;
    }

    return int.tryParse(value);
  }

List which issues are fixed by this PR. You must list at least one issue.

Sorry, I think this is such a small change that it doesn't require one. But if I really must, I'll do, of course :)

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.