Remove deprecated member type from interface def

The member types `phase_label` and `phase_sweep_policy_type` formerly
required a definition as part of the TKSVM simulation class interface.
The need for this historically originated in when classifiers and sweep
policies were determined at compile time. Now that these are derived of
abstract policies, the remaining uses of these types could be replaced
by their canonical definitions:

    using phase_label = typename phase_space::classifier::policy<phase_point>::label_type;
    using phase_sweep_policy_type = phase_space::sweep::policy<phase_point>;

TKSVM-compliant simulation classes are thus now longer required to
implement these.