build: [autodetect] -> [no] in iconv help.

configure

@@ -188,7 +188,7 @@ External library support:
   --enable-fontconfig      enable fontconfig
   --enable-frei0r          enable frei0r video filtering
   --enable-gnutls          enable gnutls [no]
-  --enable-iconv           enable iconv [autodetect]
+  --enable-iconv           enable iconv [no]
   --enable-libaacplus      enable AAC+ encoding via libaacplus [no]
   --enable-libass          enable libass subtitles rendering [no]
   --enable-libbluray       enable BluRay reading using libbluray [no]