Remove built-in Nu support in favor of extension (#10570)

Release Notes:

- Removed built-in Nu language support in favor of an extension.

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Co-authored-by: Marshall <marshall@zed.dev>

crates/extensions_ui/src/extension_suggest.rs

@@ -48,6 +48,7 @@ const SUGGESTIONS_BY_EXTENSION_ID: &[(&str, &[&str])] = &[
     ("lua", &["lua"]),
     ("make", &["Makefile"]),
     ("nix", &["nix"]),
+    ("nu", &["nu"]),
     ("ocaml", &["ml", "mli"]),
     ("php", &["php"]),
     ("prisma", &["prisma"]),