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>

crates/nu-command/tests/commands/reduce.rs

@@ -47,12 +47,12 @@ fn reduce_rows_example() {
 }
 
 #[test]
-fn reduce_numbered_example() {
+fn reduce_enumerate_example() {
     let actual = nu!(
         cwd: ".", pipeline(
         r#"
-        echo one longest three bar
-        | reduce -n { |it, acc| if ($it.item | str length) > ($acc.item | str length) {echo $it} else {echo $acc}}
+        echo one longest three bar | enumerate
+        | reduce { |it, acc| if ($it.item | str length) > ($acc.item | str length) {echo $it} else {echo $acc}}
         | get index
         "#
         )
@@ -62,12 +62,14 @@ fn reduce_numbered_example() {
 }
 
 #[test]
-fn reduce_numbered_integer_addition_example() {
+fn reduce_enumerate_integer_addition_example() {
     let actual = nu!(
         cwd: ".", pipeline(
         r#"
         echo [1 2 3 4]
-        | reduce -n { |it, acc| $acc.item + $it.item }
+        | enumerate
+        | reduce { |it, acc| { index: ($it.index) item: ($acc.item + $it.item)} }
+        | get item
         "#
         )
     );
@@ -121,11 +123,14 @@ fn error_reduce_empty() {
 }
 
 #[test]
-fn uses_optional_index_argument() {
+fn enumerate_reduce_example() {
     let actual = nu!(
         cwd: ".", pipeline(
-        r#"[18 19 20] | reduce -f 0 {|elem accum index| $accum + $index } | to nuon"#
-    ));
+        r#"
+        [one longest three bar] | enumerate | reduce {|it, acc| if ($it.item | str length) > ($acc.item | str length) { $it } else { $acc }} | get index
+        "#
+        )
+    );
 
-    assert_eq!(actual.out, "3");
+    assert_eq!(actual.out, "1");
 }