Revert "Let selected Xcode determine run destination for unit test builds."

This reverts commit 184f5b8.

Author: w-goog

.github/workflows/unit_tests.yml

@@ -62,5 +62,6 @@ jobs:
         xcodebuild \
           -scheme GoogleSignIn-Package \
           -sdk ${{ matrix.sdk }} \
+          -destination ${{ matrix.destination }} \
           test-without-building