buildroot

xserver: remove patch for aarch64

xorg-server-1.15.0.tar.gz already has full support of aarch64.
It was added with this commit http://patchwork.freedesktop.org/patch/14361/

Even though the patch in question doesn't break patching or building of xserver
it duplicates aarch64 entries in "include/servermd.h".

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>