Simplify static_assert_sizes.

We want to run them on all 64-bit platforms.

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -72,7 +72,7 @@ pub struct PendingPredicateObligation<'tcx> {
 }
 
 // `PendingPredicateObligation` is used a lot. Make sure it doesn't unintentionally get bigger.
-#[cfg(all(any(target_arch = "x86_64", target_arch = "aarch64"), target_pointer_width = "64"))]
+#[cfg(target_pointer_width = "64")]
 static_assert_size!(PendingPredicateObligation<'_>, 72);
 
 impl<'tcx> FulfillmentContext<'tcx> {