matchbox: fix dependencies

A dependency on BR2_PACKAGE_XORG7 is enough, no need to depend on
BR2_PACKAGE_XORG_XSERVER.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/matchbox/Config.in

@@ -1,6 +1,5 @@
 config BR2_PACKAGE_MATCHBOX
 	bool "MatchBox Window Manager"
-	select BR2_PACKAGE_XSERVER_XORG_SERVER
 	select BR2_PACKAGE_XORG7
 	select BR2_PACKAGE_FONTCONFIG
 	select BR2_PACKAGE_XLIB_LIBXDAMAGE