include: remove XZ host prereq

We build XZ as part of tools/, so no need to require it to be available
on the host system.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

include/prereq-build.mk

@@ -164,9 +164,6 @@ $(eval $(call SetupHostCommand,git,Please install Git (git-core) >= 1.7.12.2, \
 $(eval $(call SetupHostCommand,file,Please install the 'file' package, \
 	file --version 2>&1 | grep file))
 
-$(eval $(call SetupHostCommand,xz,Please install xz-utils, \
-	xz --version | grep XZ))
-
 ifneq ($(HOST_OS),Darwin)
 $(eval $(call SetupHostCommand,openssl,Please install the 'openssl' utility, \
 	openssl version | grep '\(OpenSSL\|LibreSSL\)'))