deprecate scm_struct_table

deprecate scm_struct_table

* libguile/goops.h:
* libguile/goops.c (scm_i_define_class_for_vtable): New internal helper,
  defines a class for a vtable, relying on the name slot being set
  correctly.
  (scm_class_of, create_struct_classes): Use the local vtable-to-class
  map instead of scm_struct_table.

* libguile/struct.h (SCM_STRUCT_TABLE_NAME, SCM_SET_STRUCT_TABLE_NAME)
  (SCM_STRUCT_TABLE_CLASS, SCM_SET_STRUCT_TABLE_CLASS, scm_struct_table)
  (scm_struct_create_handle): Deprecate these internals of the map
  between structs and classes.

* libguile/deprecated.h:
* libguile/deprecated.c (scm_struct_create_handle): Deprecated code over
  here now.