Remove deprecated commands (#14726)

# Description

Remove commands which were deprecated in 0.101:

* `split-by` (#14019)
* `date to-record` and `date to-table` (#14319)

# User-Facing Changes

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

TODO: `grep` (`ag`) doc repo for any usage of these commands

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

@@ -103,7 +103,6 @@ mod skip;
 mod sort;
 mod sort_by;
 mod source_env;
-mod split_by;
 mod split_column;
 mod split_row;
 mod str_;

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

@@ -1,66 +0,0 @@
-use nu_test_support::fs::Stub::EmptyFile;
-use nu_test_support::playground::Playground;
-use nu_test_support::{nu, pipeline};
-
-#[test]
-fn splits() {
-    let sample = r#"
-                [[first_name, last_name, rusty_at, type];
-                 [Andrés, Robalino, "10/11/2013", A],
-                 [JT, Turner, "10/12/2013", B],
-                 [Yehuda, Katz, "10/11/2013", A]]
-            "#;
-
-    let actual = nu!(pipeline(&format!(
-        r#"
-                  {sample}
-                | group-by rusty_at
-                | split-by type
-                | get A."10/11/2013"
-                | length
-            "#
-    )));
-
-    assert_eq!(actual.out, "2");
-}
-
-#[test]
-fn errors_if_no_input() {
-    Playground::setup("split_by_no_input", |dirs, _sandbox| {
-        let actual = nu!(cwd: dirs.test(), pipeline("split-by type"));
-
-        assert!(actual.err.contains("no input value was piped in"));
-    })
-}
-
-#[test]
-fn errors_if_non_record_input() {
-    Playground::setup("split_by_test_2", |dirs, sandbox| {
-        sandbox.with_files(&[
-            EmptyFile("los.txt"),
-            EmptyFile("tres.txt"),
-            EmptyFile("amigos.txt"),
-            EmptyFile("arepas.clu"),
-        ]);
-
-        let input_mismatch = nu!(cwd: dirs.test(), pipeline("5 | split-by type"));
-
-        assert!(input_mismatch.err.contains("doesn't support int input"));
-
-        let only_supports = nu!(
-            cwd: dirs.test(), pipeline(
-            "
-                ls
-                | get name
-                | split-by type
-            "
-        ));
-
-        assert!(
-            only_supports
-                .err
-                .contains("only Record input data is supported")
-                || only_supports.err.contains("expected: record")
-        );
-    })
-}