is(x = module) vs. __traits(isModule, x)

[Steven Schveighoffer]

Someone on the discord chat brought this up:

We currently have 2 ways to check if a symbol is a module:

import std.stdio;

pragma(msg, is(std.stdio == module)); // true
pragma(msg, __traits(isModule, std.stdio)); // true

Why both? The first thing that struck me is that, std.stdio is NOT a 
type. `is` specifically says it works with types. So that seems out of 
place (indeed the documentation does not mention anything special about 
this).

And then I looked up when they were added, thinking that maybe one 
predates the other, and there is a reason it didn't handle all cases.

Wrong. They were both added in the *same PR* to mean the *same thing*: 
https://github.com/dlang/dmd/pull/5290

Is there a reason we want to have both? Why did we want to muddy the 
`is` waters?

I really think we should remove one of these, I would recommend removing 
the `is` form, since it's the only exception to the rule that the 
parameter must be a type.

BTW, same with packages:

is(std == package) == __traits(isPackage, std);

-Steve