remove prohibition of unmanaged constructed types

Author: RexJaeschke

standard/types.md

@@ -639,9 +639,9 @@ unmanaged_type
     ;
 ```
 
-An *unmanaged_type* is any type that isn’t a *reference_type*, a *type_parameter*, or a constructed type, and contains no fields whose type is not an *unmanaged_type*. In other words, an *unmanaged_type* is one of the following:
+An *unmanaged_type* is any type that isn’t a *reference_type* or a *type_parameter*, and contains no fields whose type is not an *unmanaged_type*. In other words, an *unmanaged_type* is one of the following:
 
 - `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 fields of *unmanaged_type*s only.
+- Any user-defined *struct_type* that contains 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)).