For #2905: Remove device name during sync logout

app/src/main/java/org/mozilla/fenix/settings/AccountSettingsFragment.kt

@@ -59,6 +59,12 @@ class AccountSettingsFragment : PreferenceFragmentCompat(), CoroutineScope {
         override fun onLoggedOut() {
             launch {
                 Navigation.findNavController(view!!).popBackStack()
+
+                // Remove the device name when we log out.
+                context?.let {
+                    val deviceNameKey = it.getPreferenceKey(R.string.pref_key_sync_device_name)
+                    preferenceManager.sharedPreferences.edit().remove(deviceNameKey).apply()
+                }
             }
         }