remove enclosing braces from song_status_format in example config file

it's not needed here, I just didn't remove
it when I copied it from ncmpcpp sources.

doc/config

@@ -104,7 +104,7 @@
 #
 #song_list_format = "{%a - }{%t}|{$8%f$9}$R{$3(%l)$9}"
 #
-#song_status_format = "{{{%a{ \"%b\"{ (%y)}} - }{%t}}|{%f}}"
+#song_status_format = "{{%a{ \"%b\"{ (%y)}} - }{%t}}|{%f}"
 #
 #song_library_format = "{%n - }{%t}|{%f}"
 #