missing __traits(isArray, T)? what's the difference between __traits & std.traits? can we remove one to avoid dup?

[mw]

Hi,

I'm checking:

https://dlang.org/library/object/destroy.html
```
...
if (__traits(isStaticArray, T));
```
and want to try `__traits(isArray, T)` in my code, but the 
compiler complains it's not there,

Then I found std.traits.isArray!T here:

https://dlang.org/phobos/std_traits.html

which has much more traits defined than:

https://dlang.org/spec/traits.html#isStaticArray ...

I read both can be used at compile time, I'm wondering is there 
any difference between __traits & std.traits?

If there is no difference between this two mechanisms, should we 
completely move all the `__traits` stuff into std.traits to avoid 
duplication?