package/x11r7/xserver_xorg-server: remove unused configure option --disable-xsdl

Upstream removed this configure option:
https://cgit.freedesktop.org/xorg/xserver/commit/configure.ac?h=server-1.20-branch&id=52bc6d944946e66ea2cc685feaeea40bb496ea83

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 51761e0f932278784d71574343fda9b789f65885)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/x11r7/xserver_xorg-server/xserver_xorg-server.mk

@@ -91,8 +91,7 @@ ifeq ($(BR2_PACKAGE_XSERVER_XORG_SERVER_KDRIVE),y)
 XSERVER_XORG_SERVER_CONF_OPTS += \
 	--enable-kdrive \
 	--disable-glx \
-	--disable-dri \
-	--disable-xsdl
+	--disable-dri
 
 else # modular
 XSERVER_XORG_SERVER_CONF_OPTS += --disable-kdrive