Remove dead BSON related tests (#10458)

Those tests where behind a feature flag `bson` that is never defined in
`Cargo.toml`

Remove them.

crates/nu-command/tests/format_conversions/bson.rs

@@ -1,17 +0,0 @@
-#[cfg(feature = "bson")]
-#[test]
-fn table_to_bson_and_back_into_table() {
-    use nu_test_support::{nu, pipeline};
-    let actual = nu!(
-        cwd: "tests/fixtures/formats", pipeline(
-        r#"
-            open sample.bson
-            | to bson
-            | from bson
-            | get root
-            | get 1.b
-        "#
-    ));
-
-    assert_eq!(actual.out, "whel");
-}

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

@@ -1,4 +1,3 @@
-mod bson;
 mod csv;
 #[cfg(feature = "extra")]
 mod html;