[dmd-internals] Module.semantic is not virtual

[David Nadlinger via dmd-internals]

On 31 Jul 2016, at 5:18, Daniel Murphy via dmd-internals wrote:
> They're just separate functions that happen to use the same name.
> They're never going to be called through a reference typed as Dsymbol
> (I hope).

Yep. We should just rename Module.semantic.

 — David