build: clean up Package.swift slightly

Now that macros are enabled on all the platforms we currently support
(Windows, Linux, Apple), the optional addition of the macro targets was
removed.  Clean up the structure of the file as the initial changes were
done quickly to enable testing on all platforms.

Author: compnerd

Examples/Package.swift

@@ -48,11 +48,6 @@ let package = Package(
       ],
       path: "Tests/MacroExamples/Implementation"
     ),
-  ]
-)
-
-package.targets.append(
-  contentsOf: [
     .target(
       name: "MacroExamplesInterface",
       dependencies: [