Disable xenstore_dom_chmod in stubdom build.

Disable xenstore_dom_chmod in stubdom build.

This change:

    commit ad202d4194eab87d3645f13e7726a4d609e42fe8
    Author: Ian Jackson <ian.jackson@eu.citrix.com>
    Date:   Tue Jul 21 15:29:43 2009 +0100

	add per domain low level xenstore functions [PATCH 2/3]
	add per domain low level xenstore functions (read/chmod/write/watch).

broke the stubdom build because minios's fork/version of libxenstore
does not have the xenstore chmod operation.  As xenstore_dom_chmod
is not currently used in stubdom, #if it out.

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