message: Remove register_status_not_ok_type.
  Just using a try catch is simpler and more readable.
diff: @@ -18,16 +18,7 @@ from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  -from tink.python.cc.clif import status as error
  -
  -KNOWN_STATUS_NOT_OK_TYPES = (error.StatusNotOk,)
  -
  -
  -def register_status_not_ok_type(status_not_ok_type):
  - global KNOWN_STATUS_NOT_OK_TYPES
  - if status_not_ok_type not in KNOWN_STATUS_NOT_OK_TYPES:
  - assert issubclass(status_not_ok_type, Exception)
  - KNOWN_STATUS_NOT_OK_TYPES += (status_not_ok_type,)
  +from tink.python.cc.clif import status
  def use_tink_errors(func):
  @@ -35,7 +26,7 @@ def use_tink_errors(func):
  def wrapper(*args):
  try:
  return func(*args)
  - except KNOWN_STATUS_NOT_OK_TYPES as e:
  + except status.StatusNotOk as e:
  raise TinkError(e)
  return wrapper
  