Use Level::from_symbol in unnecessary_clippy_cfg

Author: flip1995

clippy_lints/src/attrs.rs

@@ -1000,9 +1000,7 @@ fn check_clippy_cfg_attr(
 ) {
     if cfg_attr.has_name(sym::clippy)
         && let Some(ident) = behind_cfg_attr.ident()
-        // FIXME: replace with `from_symbol` once https://github.com/rust-lang/rust/pull/121230
-        // is merged.
-        && Level::from_str(ident.name.as_str()).is_some()
+        && Level::from_symbol(ident.name, Some(attr.id)).is_some()
         && let Some(items) = behind_cfg_attr.meta_item_list()
     {
         let nb_items = items.len();