[core] Remove platform dance in Package.swift (#400)

Co-authored-by: Sébastien Stormacq <sebastien.stormacq@gmail.com>

NOTICE.txt

@@ -27,7 +27,7 @@ components that this product depends on.
 -------------------------------------------------------------------------------
 
 
-This product contains a derivation various scripts from SwiftNIO.
+This product contains a derivation various code and scripts from SwiftNIO.
 
   * LICENSE (Apache License 2.0):
     * https://www.apache.org/licenses/LICENSE-2.0

Package.swift

@@ -2,15 +2,9 @@
 
 import PackageDescription
 
-#if os(macOS)
-let platforms: [PackageDescription.SupportedPlatform]? = [.macOS(.v15)]
-#else
-let platforms: [PackageDescription.SupportedPlatform]? = nil
-#endif
-
 let package = Package(
     name: "swift-aws-lambda-runtime",
-    platforms: platforms,
+    platforms: [.macOS(.v15)],
     products: [
         // this library exports `AWSLambdaRuntimeCore` and adds Foundation convenience methods
         .library(name: "AWSLambdaRuntime", targets: ["AWSLambdaRuntime"]),