Remove dead code stemming from the old effects desugaring

compiler/rustc_hir_analysis/src/check/check.rs

@@ -821,8 +821,7 @@ pub(super) fn check_specialization_validity<'tcx>(
     let result = opt_result.unwrap_or(Ok(()));
 
     if let Err(parent_impl) = result {
-        // FIXME(effects) the associated type from effects could be specialized
-        if !tcx.is_impl_trait_in_trait(impl_item) && !tcx.is_effects_desugared_assoc_ty(impl_item) {
+        if !tcx.is_impl_trait_in_trait(impl_item) {
             report_forbidden_specialization(tcx, impl_item, parent_impl);
         } else {
             tcx.dcx().delayed_bug(format!("parent item: {parent_impl:?} not marked as default"));

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -2042,7 +2042,7 @@ pub(super) fn check_type_bounds<'tcx>(
     // A synthetic impl Trait for RPITIT desugaring or assoc type for effects desugaring has no HIR,
     // which we currently use to get the span for an impl's associated type. Instead, for these,
     // use the def_span for the synthesized  associated type.
-    let impl_ty_span = if impl_ty.is_impl_trait_in_trait() || impl_ty.is_effects_desugaring {
+    let impl_ty_span = if impl_ty.is_impl_trait_in_trait() {
         tcx.def_span(impl_ty_def_id)
     } else {
         match tcx.hir_node_by_def_id(impl_ty_def_id) {