mdds is header-only

Change-Id: I27e5ae913474001154fa6352a3ccefaee16e309c
(cherry picked from commit 7fffbdc4)
Reviewed-on: https://gerrit.libreoffice.org/16504Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>

RepositoryExternal.mk

@@ -132,7 +132,7 @@ endef
 else # !SYSTEM_MDDS
 
 define gb_ExternalProject__use_mdds_headers
-$(call gb_ExternalProject_use_external_project,$(1),mdds)
+$(call gb_ExternalProject_use_unpacked,$(1),mdds)
 
 endef