Rename NestedMetaItem::[Ll]iteral as NestedMetaItem::[Ll]it.

We already use a mix of `Literal` and `Lit`. The latter is better
because it is shorter without causing any ambiguity.

compiler/rustc_resolve/src/lib.rs

@@ -1989,7 +1989,7 @@ impl<'a> Resolver<'a> {
                     .find(|a| a.has_name(sym::rustc_legacy_const_generics))?;
                 let mut ret = Vec::new();
                 for meta in attr.meta_item_list()? {
-                    match meta.literal()?.kind {
+                    match meta.lit()?.kind {
                         LitKind::Int(a, _) => ret.push(a as usize),
                         _ => panic!("invalid arg index"),
                     }