Revert "require Swift 6.1"

This reverts commit 16f54b9.

Android build is still using 6.0.3, so revert this temporarily. Swift 6.1 is
still required for eLinux.

Author: lhoward

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:6.1
+// swift-tools-version:6.0
 
 import Foundation
 import PackageDescription