doc: example-config: Remove recipient_delimiter

It defaults to the global recipient_delimiter, which should always be used
anyway. Don't add confusion by documenting the legacy setting that only
exists for backwards compatibility.

doc/example-config/conf.d/90-sieve.conf

@@ -113,15 +113,6 @@ plugin {
   # The sieve_extprograms plugin is included in this release.
   #sieve_plugins =
 
-  # The separator that is expected between the :user and :detail
-  # address parts introduced by the subaddress extension. This may
-  # also be a sequence of characters (e.g. '--'). The current
-  # implementation looks for the separator from the left of the
-  # localpart and uses the first one encountered. The :user part is
-  # left of the separator and the :detail part is right. This setting
-  # is also used by Dovecot's LMTP service.
-  #recipient_delimiter = +
-
   # The maximum size of a Sieve script. The compiler will refuse to compile any
   # script larger than this limit. If set to 0, no limit on the script size is
   # enforced.