Remove iconv from required PHP modules

The usage of iconv has been removed in: nextcloud/server#29470

The dependency has been removed in: nextcloud/server#29958

Signed-off-by: MichaIng <micha@dietpi.com>

Author: MichaIng

admin_manual/installation/source_installation.rst

@@ -40,7 +40,6 @@ Required:
 * PHP module filter (only on Mageia and FreeBSD)
 * PHP module GD
 * PHP module hash (only on FreeBSD)
-* PHP module iconv
 * PHP module JSON
 * PHP module libxml (Linux package libxml2 must be >=2.7.0)
 * PHP module mbstring