Remove ParseFacebookUtils and ParseTwitterUtils

[mtrezza]

New Feature / Enhancement Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.

Current Limitation

ParseFacebookUtils and ParseTwitterUtils:

• Require frequent maintenance and updates even though they are convenience methods that save the developer just a few lines of code, in contrast to the amounts of code this requires in the SDK.
• They probably used to be the most popular 3rd party auth providers back in the days, but today that may not be true anymore. The focus on these 2 services seems increasingly arbitrary and lacks justification.
• Bundles the Facebook SDK with the Parse SDK which creates conflicts if developers use different FB SDK versions in their project.

Feature / Enhancement Description

Remove both utils. There seems to be community support as well, see #1774 (comment).

[parse-github-assistant]

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[mtrezza]

@parse-community/ios-sdk, @chriscborg, @matteolongeri-ovolab, @SOGAPPS, @gmohiuddin215, @JustinGanzer, @nmoersch-calimoto, @caliandi is everyone fine with the removal?