scmake('clean')

`scdel()` works, and `scmake()` works for normal targets. but `scmake('clean')` should probably delete the deleted targets, and it doesn't yet. same for the other cleaning targets (tidy and purge, i think)

Start by tracing the scmake() and scdel() entry points to understand how normal targets and deleted targets are handled. Check the existing behavior for the clean target, then determine whether tidy and purge follow the same path. Done means scmake('clean'), and the applicable other cleaning targets, delete the intended deleted targets consistently.

Written by the indexing model from the issue text.