WireGuardApp: integrate WireGuardKit sources directly

Signed-off-by: Andrej Mihajlov <and@mullvad.net>

Sources/WireGuardKit/PacketTunnelSettingsGenerator.swift

@@ -4,7 +4,10 @@
 import Foundation
 import Network
 import NetworkExtension
+
+#if SWIFT_PACKAGE
 import WireGuardKitC
+#endif
 
 class PacketTunnelSettingsGenerator {
     let tunnelConfiguration: TunnelConfiguration

Sources/WireGuardKit/PrivateKey.swift

@@ -2,7 +2,10 @@
 // Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
 
 import Foundation
+
+#if SWIFT_PACKAGE
 import WireGuardKitC
+#endif
 
 /// The class describing a private key used by WireGuard.
 public class PrivateKey: BaseKey {

Sources/WireGuardKit/WireGuardAdapter.swift

@@ -3,7 +3,10 @@
 
 import Foundation
 import NetworkExtension
+
+#if SWIFT_PACKAGE
 import WireGuardKitGo
+#endif
 
 public enum WireGuardAdapterError: Error {
     /// Failure to locate tunnel file descriptor.