build: remove Linux kernel build integration.

We haven't shipped a XenoLinux kernel for more releases than I can remember.
We held onto these because osstest was using them but this is no longer the
case.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

config/Linux.mk

@@ -1,8 +1 @@
 include $(XEN_ROOT)/config/StdGNU.mk
-
-# You may use wildcards, e.g. KERNELS=*2.6*
-KERNELS ?= 
-
-XKERNELS := $(foreach kernel, $(KERNELS), \
-              $(patsubst buildconfigs/mk.%,%, \
-                $(wildcard buildconfigs/mk.$(kernel))) )