Delete swift-4.2

Package@swift-4.2.swift

@@ -1,19 +0,0 @@
-// swift-tools-version:4.2
-
-import PackageDescription
-
-let package = Package(
-  name: "CryptoSwift",
-  products: [
-    .library(
-      name: "CryptoSwift",
-      targets: ["CryptoSwift"]
-    )
-  ],
-  targets: [
-    .target(name: "CryptoSwift"),
-    .testTarget(name: "Tests", dependencies: ["CryptoSwift"]),
-    .testTarget(name: "TestsPerformance", dependencies: ["CryptoSwift"])
-  ],
-  swiftLanguageVersions: [.v4, .v4_2]
-)