Fix WPML Appointment - to not have duplicates

[Valentina R]

Customer suggests we look into how YITH Bookings does the booking with WPML. Not having duplicates could solve some issues.

Proposed here: https://bookingwp.com/forums/topic/managing-appointments-admin/#post-178665

[Željan Topić]

Removed duplicated appointments from 4.1.5