Get rid of tcm_smart from TyCoMapper

Following a succession of refactorings of the type checker, culminating in the patch Make a smart mkAppTyM we have got rid of mkNakedAppTy etc. And that in turn meant that the tcm_smart field of the generic TyCoMapper (in Type.hs) was entirely unused. It was always set to True.

So this patch just gets rid of it completely. Less code, less complexity, and more efficient because fewer higher-order function calls. Everyone wins.

No change in behaviour; this does not cure any bugs!