package/sdl_mixer: drop unrecognized option

--without-x is not recognized since at least version 1.2.12:

configure: WARNING: unrecognized options: --disable-gtk-doc, --disable-gtk-doc-html, --disable-doc, --disable-docs, --disable-documentation, --with-xmlto, --with-fop, --enable-ipv6, --disable-nls, --without-x

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/sdl_mixer/sdl_mixer.mk

@@ -23,7 +23,6 @@ SDL_MIXER_DEPENDENCIES = sdl
 SDL_MIXER_AUTORECONF = YES
 
 SDL_MIXER_CONF_OPTS = \
-	--without-x \
 	--with-sdl-prefix=$(STAGING_DIR)/usr \
 	--disable-music-mod \
 	--disable-music-mp3 \