GB-090 21.3.5.4 [meta.unary. prop] Unnecessary precondition for is_aggregate

The precondition for is_aggregate is "`remove_all_extents_t<T>` shall be a complete type or `cv void`." This means that `is_aggregate_v<Incomplete[2]>` is undefined, but an array is always an aggregate, we don't need a complete element type to know that.

Suggestion: T shall be a complete type, an array, or cv void.