Revert "Support cross compilation in macOS toolchain builds (#62306)"

[ethan-kusters]

This reverts commit a36ab6e.

The change to support cross compilation of docc in macOS toolchains is breaking nightly toolchain builds – this will unblock them.

From: https://ci.swift.org/job/oss-swift-package-macos/1265/console

** Building swift-docc **
+ /Users/ec2-user/jenkins/workspace/oss-swift-package-macos/swift-docc/build-script-helper.py test --toolchain /Users/ec2-user/jenkins/workspace/oss-swift-package-macos/build/buildbot_osx/intermediate-install/macosx-x86_64/Applications/Xcode.app/Contents/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2022-12-02-a.xctoolchain/usr --configuration release --build-dir /Users/ec2-user/jenkins/workspace/oss-swift-package-macos/build/buildbot_osx/unified-swiftpm-build-macosx-x86_64 --multiroot-data-file /Users/ec2-user/jenkins/workspace/oss-swift-package-macos/swift/utils/build_swift/resources/SwiftPM-Unified-Build.xcworkspace --cross-compile-hosts macosx-arm64 --update
warning: --multiroot-data-file is an *unsupported* option which can be removed at any time; do not rely on it
warning: 'swiftpm': failed to retrieve search paths with pkg-config; maybe pkg-config is not installed
warning: 'swiftpm': couldn't find pc file for sqlite3
warning: 'swiftpm': couldn't find pc file for sqlite3
error: Could not find target named 'SwiftDocCPackageTests_7C0DE4B8BA63A33A_PackageProduct'
error: fatalError
FAIL: Testing swift-docc failed

It looks like the --test-product option Swift-DocC's build script passes to SwiftPM is supported when building for multiple architectures but not when testing. PR toolchain builds don't run tests which is why this wasn't caught before merging.

Resolves rdar://102908495

[ethan-kusters]

@swift-ci please smoke test