Fix issue for Jetpack CP sites

`isUsingWpComRestApi` was returning false for Jetpack CP sites, leading to always ignoring saved app passwords credentials, as for WPCom rest sites, `SiteModel#username` is always null.

Author: hichamboushaba

libs/fluxc/src/main/java/org/wordpress/android/fluxc/model/SiteModel.java

@@ -787,7 +787,7 @@ public void setOrigin(@SiteOrigin int origin) {
     }
 
     public boolean isUsingWpComRestApi() {
-        return isWPCom() || (isJetpackConnected() && getOrigin() == ORIGIN_WPCOM_REST);
+        return isWPCom() || getOrigin() == ORIGIN_WPCOM_REST;
     }
 
     public void setSpaceAvailable(long spaceAvailable) {

libs/fluxc/src/main/java/org/wordpress/android/fluxc/network/rest/wpapi/applicationpasswords/ApplicationPasswordsStore.kt

@@ -39,7 +39,7 @@ class ApplicationPasswordsStore @Inject constructor(
         val uuid = encryptedPreferences.getString(site.uuidPrefKey, null)
 
         return when {
-            !site.isUsingWpComRestApi && site.username != username -> null
+            site.username != username && !site.isUsingWpComRestApi -> null
             username != null && password != null ->
                 ApplicationPasswordCredentials(
                     userName = username,