Description

Removes the old alias implementation.

The only remaining issues with the new alias implementation is missing completions with external completers and no support for aliasing a call with env shorthand (alias foo = FOO=bar run-something). Also some presentation issues, like which and wrong usage. I think these are not deal breakers and we can go ahead with the removal.

User-Facing Changes

old-alias is no longer available.

Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

• cargo fmt --all -- --check to check standard code formatting (cargo fmt --all applies these changes)
• cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A clippy::needless_collect to check that you're using the standard code style
• cargo test --workspace to check that all tests pass
• cargo run -- crates/nu-utils/standard_library/tests.nu to run the tests for the standard library

Note
from nushell you can also use the toolkit as follows

use toolkit.nu  # or use an `env_change` hook to activate it automatically
toolkit check pr

After Submitting

If your PR had any user-facing changes, update the documentation after the PR is merged, if necessary. This will help us keep the docs up to date.