auto-sub: Code simplification

With a little change to maybe-sub, which makes it call the
todo-function with only two params: the original function and a vector
of task, project and args, we can simplify the code by completely
removing apply-this-task (replaced by apply itself).

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
auto-sub: Further code cleanup

We don't need the when wrapping in apply-sub-tasks either, maybe-sub
takes care of that already. While there, move the with-subs to
maybe-sub too.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>