Remove useless calls to assemble_extension_candidates_for_traits_in_scope

Calls to `assemble_extension_candidates_for_traits_in_scope` with
`DUMMY_HIR_ID` as `expr_hir_id` are useless because the first thing
that this function does is to return `Ok(())` in this case.

Author: marmeladema

src/librustc_typeck/check/method/probe.rs

@@ -1513,7 +1513,6 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             );
             pcx.allow_similar_names = true;
             pcx.assemble_inherent_candidates();
-            pcx.assemble_extension_candidates_for_traits_in_scope(hir::DUMMY_HIR_ID)?;
 
             let method_names = pcx.candidate_method_names();
             pcx.allow_similar_names = false;
@@ -1523,10 +1522,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     pcx.reset();
                     pcx.method_name = Some(method_name);
                     pcx.assemble_inherent_candidates();
-                    pcx.assemble_extension_candidates_for_traits_in_scope(hir::DUMMY_HIR_ID)
-                        .map_or(None, |_| {
-                            pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
-                        })
+                    pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
                 })
                 .collect();