Remove unnecessary Package.swift conditional

Author: tbkka

Package.swift

@@ -1,4 +1,3 @@
-// swift-tools-version:3.1
 // Package.swift - description
 //
 // Copyright (c) 2014 - 2016 Apple Inc. and the project authors
@@ -10,20 +9,6 @@
 
 import PackageDescription
 
-#if swift(>=3.1)
-let package = Package(
-  name: "SwiftProtobuf",
-  targets: [
-    Target(name: "PluginLibrary",
-           dependencies: ["SwiftProtobuf"]),
-    Target(name: "protoc-gen-swift",
-           dependencies: ["PluginLibrary", "SwiftProtobuf"]),
-    Target(name: "Conformance",
-           dependencies: ["SwiftProtobuf"]),
-  ],
-  swiftLanguageVersions: [3, 4]
-)
-#else
 let package = Package(
   name: "SwiftProtobuf",
   targets: [
@@ -35,4 +20,3 @@ let package = Package(
            dependencies: ["SwiftProtobuf"]),
   ]
 )
-#endif