Revert TODOs related to in-progress briefcase work.

[freakboy3742]

Now that the framework-based support is all in place, we can revert the TODOs that tied the usage of Briefcase to the in-progress branches.

This can't be merged until full binary support is restored to beeware/Python-support-testbed (see beeware/Python-support-testbed#49).

When this PR is merged, we can delete the branches associated with:

• Switch to a dynamic framework. briefcase-macOS-Xcode-template#47
• Modifications to support framework-style packaging. briefcase-macOS-app-template#64
• Switch to dynamic framework builds briefcase-iOS-Xcode-template#37
• Drop Python 3.8 support and bump macOS/iOS template epoch briefcase#1934

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct