feat(appsflyer): added registerUninstall function (#3401)

* fix(appsflyer): added missing registerUninstall()

According to appsflyer docs, there should be *registerUninstall()* method to allow tracking uninstalls for iOS:

https://github.com/AppsFlyerSDK/appsflyer-cordova-plugin/blob/master/docs/API.md#-registeruninstalltoken-void

* fixed asterisk alignment to pass CI test

* removed whitespace to pass CI test

src/@ionic-native/plugins/appsflyer/index.ts

@@ -137,6 +137,13 @@ export class Appsflyer extends IonicNativePlugin {
   @Cordova({ sync: true })
   updateServerUninstallToken(token: string): void {}
 
+  /**
+   * (iOS) Allows to pass APN Tokens that where collected by third party plugins to the AppsFlyer server. Can be used for Uninstall Tracking.
+   * @param {string} token APN Token
+   */
+  @Cordova({ sync: true })
+  registerUninstall(token: string): void {}
+
   /**
    * Get AppsFlyer’s proprietary Device ID. The AppsFlyer Device ID is the main ID used by AppsFlyer in Reports and APIs.
    */