remove prohibition of unmanaged constructed types

Author: RexJaeschke

standard/types.md

@@ -701,3 +701,4 @@ An *unmanaged_type* is any type that isn’t a *reference_type*, a *type_paramet
 - `sbyte`, `byte`, `short`, `ushort`, `int`, `uint`, `long`, `ulong`, `char`, `float`, `double`, `decimal`, or `bool`.
 - Any *enum_type*.
 - Any user-defined *struct_type* that is not a constructed type and contains instance fields of *unmanaged_type*s only.
+- In unsafe code ([§22.2](unsafe-code.md#222-unsafe-contexts)), any *pointer_type* ([§22.3](unsafe-code.md#223-pointer-types)).