Remove deprecated --numbered flag from four commands (#7777)

# Description

Remove `--numbered` from ~~`for`~~, `each`, `par-each`, `reduce` and
`each while`. These all provide indexes (numbering) via the optional
second param to their closures.

EDIT: Closes #6986.

# User-Facing Changes

Every command that had `--numbered` listed as "deprecated" in their help
docs is affected.

# 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.

---------

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>

src/tests/test_iteration.rs

@@ -3,7 +3,7 @@ use crate::tests::{run_test, TestResult};
 #[test]
 fn better_block_types() -> TestResult {
     run_test(
-        r#"([1, 2, 3] | each -n { |it| $"($it.index) is ($it.item)" }).1"#,
+        r#"([1, 2, 3] | enumerate | each { |e| $"($e.index) is ($e.item)" }).1"#,
         "1 is 2",
     )
 }
@@ -35,7 +35,7 @@ fn row_condition2() -> TestResult {
 #[test]
 fn par_each() -> TestResult {
     run_test(
-        r#"1..10 | par-each --numbered { |it| ([[index, item]; [$it.index, ($it.item > 5)]]).0 } | where index == 4 | get item.0"#,
+        r#"1..10 | enumerate | par-each { |it| ([[index, item]; [$it.index, ($it.item > 5)]]).0 } | where index == 4 | get item.0"#,
         "false",
     )
 }

src/tests/test_parser.rs

@@ -147,8 +147,8 @@ fn bad_var_name2() -> TestResult {
 #[test]
 fn long_flag() -> TestResult {
     run_test(
-        r#"([a, b, c] | each --numbered { |it| if $it.index == 1 { 100 } else { 0 } }).1"#,
-        "100",
+        r#"([a, b, c] | enumerate | each --keep-empty { |e| if $e.index != 1 { 100 }}).1 | to nuon"#,
+        "null",
     )
 }