libs/toolcore: don't install xentoolcore_internal.h anymore

With "xentoolcore_internal.h" been in LIBHEADER, it was installed. But
its dependency "_xentoolcore_list.h" wasn't installed so the header
couldn't be used anyway.

This patch also mean that the rule "headers.chk" doesn't check it
anymore as well.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>

tools/libs/toolcore/Makefile

@@ -5,7 +5,7 @@ MAJOR	= 1
 MINOR	= 0
 AUTOINCS := $(XEN_INCLUDE)/_xentoolcore_list.h
 
-LIBHEADER := xentoolcore.h xentoolcore_internal.h
+LIBHEADER := xentoolcore.h
 
 SRCS-y	+= handlereg.c