package/x11r7/xserver_xorg-server: fix xlib_libXfont2 dependency

package/x11r7/xserver_xorg-server: fix xlib_libXfont2 dependency

The dependency to xlib_libXfont2 was mistakenly removed in
https://git.buildroot.net/buildroot/commit/?id=e6dc4f1857eed27a19abd57fae7428bea38b69e5

Add it back again to fix build errors detected by the autobuilders and
remove handling of xlib_libXfont as well because only older versions of
xserver_xorg-server needed it.

Fixes:
http://autobuild.buildroot.net/results/f72/f72cc9b30e55e2c665de7a00482a1c3ba702118c/
http://autobuild.buildroot.net/results/9dd/9dd99e633dee8f11e7b2b973d4a72e51a2812ec9/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>