Switch to using Client from twilio.rest rather than the deleted TwillioRestClient

[rohankapoorcom]

Description:

Twilio changed the class that needs to be used from TwilioRestClient to Client. Source.

This broke after the twilio client was upgraded in #17424 and an API change was missed.

Related issue (if applicable): fixes #17871

This one is affecting 0.81.x and should be shipped in the next bugfix release. However, I'm not sure how to do that since the component itself was rewritten in #17715 (so the files are not in the same place in dev and master). This pull request is targeted at master in case that helps for the hotfix and #17883 is targeted at dev which should fix it for 0.82.0

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

[houndci-bot]

Some files could not be reviewed due to errors:

Traceback (most recent call last):

Traceback (most recent call last):
  File "/home/linters/.local/bin/flake8", line 7, in 
    from flake8.main.cli import main
ModuleNotFoundError: No module named 'flake8'

[bachya]

Make sure to base your PR against dev, not master.

[rohankapoorcom]

@bachya please read the last paragraph before the checklist. There's one pull request against master and another against dev because the code got moved around in dev and we need to hotfix the release as well as fix dev.

Please let me know if there's a better approach for this.

[balloob]

Changing to RC. Will probably be nasty when we merge master back in to dev, but we'll survive.

[rohankapoorcom]

Thanks! I'm expecting it to be annoying, but couldn't think of a way to avoid it. Let me know if I can help with the merge.