chore(spm): drop in-repo SPM example xcodeprojs from rn-tester/helloworld

The `*-SPM.xcodeproj` projects (+ their app-local Package.swift) added to
the example apps were untested demo scaffolding — no CI job builds them.
In helloworld they also broke `test_ios_helloworld`: two `.xcodeproj` in
`ios/` made CocoaPods unable to auto-select the project ("Could not
automatically select an Xcode project") during `pod install`.

Remove Helloworld-SPM.xcodeproj and RNTester-SPM.xcodeproj plus their
Package.swift, and revert the SPM-artifact lines from the .gitignore
files. The rn-tester TestLibrary example and SPM tooling are unaffected.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: chrfalch

packages/rn-tester/.gitignore

@@ -1,8 +1,2 @@
 rntesterIOS.xcodeproj.local/
 rn-tester.xcodeproj.local/
-
-# SPM – auto-generated at build time (do not commit)
-Package.resolved
-build/generated/
-build/xcframeworks/
-.build/