Add: delete_registrant method

[iamtakagi]

Add necessary delete method /meetings/{meetingId}/registrants/{registrantId}

[prschmid]

Thank you for taking on this work and adding this new functionality! I just took a quick look and it looks like there are some formatting issues and a failing test. Please let me know when you get that all fixed up and I'll happily merge this in. Thank you!

(zoomus) prschmid (~/Development/zoomus:[iamtakagi/develop]) # black . --check                                                          
would reformat docs/source/conf.py
would reformat tests/zoomus/components/meeting/test_delete_registrant.py
would reformat zoomus/components/meeting.py
Oh no! 💥 💔 💥
3 files would be reformatted, 95 files would be left unchanged.

(zoomus) prschmid (~/Development/zoomus:[iamtakagi/develop]) # nosestests
zsh: command not found: nosestests
(zoomus) prschmid (~/Development/zoomus:[iamtakagi/develop]) # nosetests  .
...........................................F...................................................................................................................................................................................................................................................................S.S......
======================================================================
FAIL: test_requires_registrant_id (tests.zoomus.components.meeting.test_delete_registrant.DeleteRegistrantV2TestCase)
----------------------------------------------------------------------
ValueError: 'id' must be set

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/prschmid/Development/zoomus/tests/zoomus/components/meeting/test_delete_registrant.py", line 42, in test_requires_registrant_id
    self.component.delete_registrant()
AssertionError: "'registrant_id' must be set" does not match "'id' must be set"

Name                                Stmts   Miss Branch BrPart  Cover
---------------------------------------------------------------------
zoomus/__init__.py                      5      0      0      0   100%
zoomus/client.py                       54      1      2      0    98%
zoomus/components/__init__.py           2      0      0      0   100%
zoomus/components/base.py              13      0      4      0   100%
zoomus/components/contacts.py          12      0      0      0   100%
zoomus/components/group.py             24      0      0      0   100%
zoomus/components/live_stream.py       10      0      0      0   100%
zoomus/components/meeting.py           65      2     10      0    97%
zoomus/components/metric.py            22      0      0      0   100%
zoomus/components/past_meeting.py      16      0      0      0   100%
zoomus/components/phone.py             15      0      0      0   100%
zoomus/components/recording.py         34      0      8      0   100%
zoomus/components/report.py            42      2      0      0    95%
zoomus/components/user.py              52      0      0      0   100%
zoomus/components/webinar.py           75      0     10      0   100%
zoomus/util.py                         94      0     38      2    98%
---------------------------------------------------------------------
TOTAL                                 535      5     72      2    99%
----------------------------------------------------------------------
Ran 312 tests in 1.125s

FAILED (SKIP=2, failures=1)