KeyError: 'private': remove private key requirement from bugbot/round_robin.py

[benjaminmah]

Currently in bugbot/round_robin.py under the class RotationDefinitions, we retrieve the private key from config.json. We do not require that and thus should be removed.

https://github.com/mozilla/bugbot/blob/master/bugbot/round_robin.py#L221

2024-05-08 13:52:50,200 - INFO - Run rule triage_owner_rotations.py
2024-05-08 13:52:50,203 - CRITICAL - Uncaught exception
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/home/bugbot/bugbot/rules/triage_owner_rotations.py", line 104, in <module>
    TriageOwnerRotations().run()
    ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/bugbot/bugbot/rules/triage_owner_rotations.py", line 38, in __init__
    self.component_triagers = ComponentTriagers(excluded_teams=excluded_teams)
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/bugbot/bugbot/component_triagers.py", line 30, in __init__
    self.round_robin: RoundRobin = RoundRobin.get_instance()
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/bugbot/bugbot/round_robin.py", line 43, in get_instance
    RoundRobin._instances[None] = RoundRobin()
                                  ^^^^^^^^^^^^
  File "/home/bugbot/bugbot/round_robin.py", line 30, in __init__
    RotationDefinitions()
  File "/home/bugbot/bugbot/round_robin.py", line 221, in __init__
    self.definitions_url = utils.get_private()["round_robin_sheet"]
                           ^^^^^^^^^^^^^^^^^^^
  File "/home/bugbot/bugbot/utils.py", line 158, in get_private
    return json.load(In)["private"]
           ~~~~~~~~~~~~~^^^^^^^^^^^
KeyError: 'private'