docs: remove Twilio insiders program note

[JenniferMah]

Remove Twilio insiders program note since the program has been on hold.
Slack: https://twilio.slack.com/archives/CGQPL0RPH/p1652909106203359

Fixes

A short description of what this PR does.

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• I have added inline documentation to the code I modified

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[sonarcloud]

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