Use Error in connect|disconnect methods in AccountServiceRemoteREST

Instead of `NSError`. This way, we'll be able to pass the error to the
`WordPressComRESTAPIInterfacing` version without needing to make any
conversion.

As far as I could see, the only consumer already worked in terms of
`Error`.
https://github.com/wordpress-mobile/WordPressAuthenticator-iOS/blob/30aada20beb9e0871f4da35a5634501536898b3b/WordPressAuthenticator/Services/WordPressComAccountService.swift#L31-L44

Author: mokagio

Sources/WordPressKit/Services/AccountServiceRemoteREST+SocialService.swift

@@ -23,7 +23,7 @@ extension AccountServiceRemoteREST {
                                        oAuthClientID: String,
                                        oAuthClientSecret: String,
                                        success: @escaping (() -> Void),
-                                       failure: @escaping ((NSError) -> Void)) {
+                                       failure: @escaping ((Error) -> Void)) {
         let path = self.path(forEndpoint: "me/social-login/connect", withVersion: ._1_1)
 
         var params = [
@@ -65,7 +65,7 @@ extension AccountServiceRemoteREST {
     ///     - oAuthClientSecret The WPCOM REST API client secret.
     ///     - success The block that will be executed on success.
     ///     - failure The block that will be executed on failure.
-    public func disconnectFromSocialService(_ service: SocialServiceName, oAuthClientID: String, oAuthClientSecret: String, success: @escaping(() -> Void), failure: @escaping((NSError) -> Void)) {
+    public func disconnectFromSocialService(_ service: SocialServiceName, oAuthClientID: String, oAuthClientSecret: String, success: @escaping(() -> Void), failure: @escaping((Error) -> Void)) {
         let path = self.path(forEndpoint: "me/social-login/disconnect", withVersion: ._1_1)
         let params = [
             "client_id": oAuthClientID,