Use default twilio client

[timmydoza]

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This PR updates the recording rules function so that it uses the twilio client that is returned by context.getTwilioClient(), instead of importing its own version with require.

It turns out, that the version of the twilio client returned by getTwilioClient() is determined by the twilio version specified in the package.json file that is used for deploying the functions (which can be found here). So it was never necessary to require('twilio') in order to get a version of the twilio client that had support for the recording rules API.