[DO NOT REVIEW] Fix TestFlight Warnings

[scannillo]

Reason for changes

See TestFlight warning from email:

Summary of changes

• Remove MacOS support from Demo application target & PayPal.xcodeproj

Checklist

• ~Added a changelog entry~

Authors

@scannillo

[scannillo]

Closing. The resolution in this SO post fixed the issue, since MXO doesn't support MacOS via SPM.

I'm leaving the build settings as-is, in case we do want to test for MacOS at a later point.