Report only top-most deprecated module import

Fixes issue 13582

https://issues.dlang.org/show_bug.cgi?id=13582
> And why you need to trace the import chain?

One simple example:

1) deprecated module A imports non-deprecated `package.d`
2) `package.d` imports deprecated module B
3) two deprecation messages get printed

I believe my rule is much more simple, and clearly shorter : "if module A is deprecated, any imports of deprecated modules from it are not warned about (transitively)".

> current dmd front-end does not have enough information to trace import chai

? But isn't it exactly what this snippet does? `Module::scope` contains scope this module was originally imported from. Which has own `module` field and so on up to the root module.