Remove the 'env' command, as we have the variable (#8185)

# Description

Removes the `env` command, as the `$env` is generally a much better
experience.

# User-Facing Changes

Breaking change: Removes `env`.

# 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

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/default_context.rs

@@ -343,7 +343,6 @@ pub fn create_default_context() -> EngineState {
 
         // Env
         bind_command! {
-            Env,
             ExportEnv,
             LetEnv,
             LoadEnv,