When Zabbix imports a map template, the each icons are created twice at same coordinate point.

[How to reproduce]
(1) Make a map as "01_map_before_export.png" and export it.
(2) Delete the map.
(3) Import the exported map.
(4) Then, we get a map with duplicated icons as "02_map_after_import.png".
I dragged the duplicated icons as easy to understand, though the icons were made at same coordinate point.

[why it occurs]
In frontends/php/include/export.inc.php:784, there is CMap::addElements.
In frontends/php/api/classes/class.cmap.php:587, there is also self::addElements which is CMap::addElements.
When importing map, the both above two codes are called.
So, the each icons are created twice.

I made a patch for removing self::addElements at frontends/php/api/classes/class.cmap.php:587.