Re-enable some good tests, remove some bad tests (#7875)

I tackled some of the disabled `FIXME`/`#[ignore]` tests. Most were
straightforward to re-enable, and a few of them did not deserve to be
re-enabled.

---------

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

tests/shell/pipeline/commands/internal.rs

@@ -704,20 +704,6 @@ fn index_out_of_bounds() {
     assert!(actual.err.contains("too large"));
 }
 
-//FIXME: jt - umm, do we actually want to support this?
-#[ignore]
-#[test]
-fn dash_def() {
-    let actual = nu!(
-        cwd: ".",
-        r#"
-            def - [x, y] { $x - $y }; - 4 1
-        "#
-    );
-
-    assert_eq!(actual.out, "3");
-}
-
 #[test]
 fn negative_decimal_start() {
     let actual = nu!(