Remove unused match pattern for primitive types

Author: GuillaumeGomez

src/librustdoc/json/conversions.rs

@@ -252,7 +252,7 @@ pub(crate) fn from_item_id_with_name(item_id: ItemId, tcx: TyCtxt<'_>, name: Opt
         ItemId::Auto { for_, trait_ } => {
             Id(format!("a:{}-{}", DisplayDefId(trait_, tcx, None), DisplayDefId(for_, tcx, name)))
         }
-        ItemId::Primitive(ty, krate) => Id(format!("p:{}:{}", krate.as_u32(), ty.as_sym())),
+        ItemId::Primitive(_, _) => unreachable!(),
     }
 }