rustdoc: Stop treating Self as a generic in search index

We already have special-cased code to handle inlining `Self` as the type
or trait it refers to, and this was just causing glitches like the
search `A -> B` yielding blanket `Into` impls.

Author: camelid

src/librustdoc/html/render/search_index.rs

@@ -852,14 +852,9 @@ fn simplify_fn_type<'tcx, 'a>(
         (false, arg)
     };
 
-    let as_arg_s = |t: &Type| match *t {
-        Type::Generic(arg_s) => Some(arg_s),
-        Type::SelfTy => Some(kw::SelfUpper),
-        _ => None,
-    };
     // If this argument is a type parameter and not a trait bound or a type, we need to look
     // for its bounds.
-    if let Some(arg_s) = as_arg_s(arg) {
+    if let Type::Generic(arg_s) = *arg {
         // First we check if the bounds are in a `where` predicate...
         let mut type_bounds = Vec::new();
         for where_pred in generics.where_predicates.iter().filter(|g| match g {