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>

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

@@ -28,8 +28,6 @@ fn skip_cell_rejection() {
     assert_eq!(actual.out, "txt");
 }
 
-// FIXME: needs more work
-#[ignore]
 #[test]
 fn complex_nested_columns() {
     let actual = nu!(cwd: ".", pipeline(