WireGuadKit: Rename WireGuardAdapter.version -> .backendVersion & remove `var wireGuardVersion` with WireGuardKit.swift

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

Sources/WireGuardKit/WireGuardAdapter.swift

@@ -56,7 +56,7 @@ public class WireGuardAdapter {
     }
 
     /// Returns a WireGuard version.
-    class var version: String {
+    class var backendVersion: String {
         return String(cString: wgVersion())
     }
 

Sources/WireGuardKit/WireGuardKit.swift

@@ -1,8 +0,0 @@
-// SPDX-License-Identifier: MIT
-// Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
-
-import Foundation
-
-public var wireGuardVersion: String {
-    return WireGuardAdapter.version
-}