Revert "Update test suite to nightly-2021-05-18"

This reverts commit 1971314.

The corresponding AST change was reverted upstream in
rust-lang/rust@91feb76

tests/common/eq.rs

@@ -425,9 +425,8 @@ spanless_eq_enum!(PatKind; Wild Ident(0 1 2) Struct(0 1 2 3) TupleStruct(0 1 2)
     Or(0) Path(0 1) Tuple(0) Box(0) Ref(0 1) Lit(0) Range(0 1 2) Slice(0) Rest
     Paren(0) MacCall(0));
 spanless_eq_enum!(TyKind; Slice(0) Array(0 1) Ptr(0) Rptr(0 1) BareFn(0) Never
-    Tup(0) AnonymousStruct(0 1) AnonymousUnion(0 1) Path(0 1) TraitObject(0 1)
-    ImplTrait(0 1) Paren(0) Typeof(0) Infer ImplicitSelf MacCall(0) Err
-    CVarArgs);
+    Tup(0) Path(0 1) TraitObject(0 1) ImplTrait(0 1) Paren(0) Typeof(0) Infer
+    ImplicitSelf MacCall(0) Err CVarArgs);
 
 impl SpanlessEq for Ident {
     fn eq(&self, other: &Self) -> bool {