This free WPML Addon removes the WP Menus Sync sub menu from the WPML sidebar menu in the backend.
Go to Plugins > Add New in your WordPress Dashboard, do a search for "so remove wpml menu sync" and install it.
… OR …
Download zip file.
Upload the zip file via the Plugins > Add New > Upload page … OR … unpack and upload with your favourite FTP client to the /plugins/ folder.
Activate the plugin on the Plugins page.