Fixed up iOS 14.5 SDK

[PoomSmart]

What does this implement/fix? Explain your changes.

• Removed its own c++ header in response of https://github.com/theos/sdks/issues/50
• Removed allowable_clients from commonly used TBD files so that anything may link to them

Does this close any currently open issues?

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Any relevant logs, error output, etc?

Any other comments?

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Where has this been tested?

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[L1ghtmann]

Given that they're identically issues, this will also resolve #49.

[PoomSmart]

@L1ghtmann Likely.