Redundancy of DRuntime and Phobos

[Q. Schroll]

I noticed that `core.internal.traits` contains a lot of stuff 
that is exactly the same in `std.traits` and `std.meta`. Is that 
for legacy reasons or should new additions be also redundant (and 
why)?

For example, there's redundant `AliasSeq` which I understand 
because it's kind of trivial and public-importing is on par with 
it. (I'd still prefer the import.)
Another example is `Unconst`, `Unqual`, 
`hasElaborate`*`Whatever`* that use a public import, but for 
whatever reason, they encapsulate the import and make an 
unnecessary template instance. None simply do
```D
public import core.internal.traits : Unconst;
```
but follow the pattern
```D
template Unconst(T)
{
     import core.internal.traits : CoreUnconst = Unconst;
     alias Unconst = CoreUnconst!(T);
}
```
I guess there's a good reason to do this and I'd like to 
understand.

In `core.internal.traits` there is a lot of stuff commented with 
"taken from". Why all this duplication? Are PRs to Phobos welcome 
that public-import the `core` stuff? Are PRs to DRuntime welcome 
that move improved stuff from Phobos to it (and replace the 
Phobos stuff by a public import)?