Rollup merge of #83055 - aDotInTheVoid:selective-strip-item-doc, r=jyn514

[rustdoc] Don't document stripped items in JSON renderer.

Fixes #80664, see [my comment there](https://github.com/rust-lang/rust/issues/80664#issuecomment-797557948) for why

Note that we already do something similar in `convert_item`:

bb4cdf8ec0/src/librustdoc/json/conversions.rs (L28-L31)

``@rustbot`` modify labels: +T-rustdoc +A-rustdoc-json

r? ``@jyn514``
cc ``@CraftSpider``

src/librustdoc/json/mod.rs

@@ -129,6 +129,8 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
         "json"
     }
 
+    const RUN_ON_MODULE: bool = false;
+
     fn init(
         krate: clean::Crate,
         options: RenderOptions,
@@ -169,8 +171,10 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
                 e.impls = self.get_impls(id)
             }
             let removed = self.index.borrow_mut().insert(from_def_id(id), new_item.clone());
+
             // FIXME(adotinthevoid): Currently, the index is duplicated. This is a sanity check
-            // to make sure the items are unique.
+            // to make sure the items are unique. The main place this happens is when an item, is
+            // reexported in more than one place. See `rustdoc-json/reexport/in_root_and_mod`
             if let Some(old_item) = removed {
                 assert_eq!(old_item, new_item);
             }