rustdoc: Remove top-level wrappers for ImplKind methods

The `ImplKind` methods can just be used directly instead.

src/librustdoc/formats/cache.rs

@@ -228,7 +228,7 @@ impl<'a, 'tcx> DocFolder for CacheBuilder<'a, 'tcx> {
         // Collect all the implementors of traits.
         if let clean::ImplItem(ref i) = *item.kind {
             if let Some(trait_) = &i.trait_ {
-                if !i.is_blanket_impl() {
+                if !i.kind.is_blanket() {
                     self.cache
                         .implementors
                         .entry(trait_.def_id())