CORD-1592: Fix wrong import of service models from core, such as in A-CORD

Change-Id: I618e78ded7cdcc0540722497c6d682156275ece0
diff --git a/xos/genx/targets/service.xtarget b/xos/genx/targets/service.xtarget
index 01e2775..ebb3e14 100644
--- a/xos/genx/targets/service.xtarget
+++ b/xos/genx/targets/service.xtarget
@@ -21,7 +21,9 @@
 {%- for b in m.bases -%}
 {%- if b!='PlCoreBase' and 'Mixin' not in b -%}
 #from core.models.{{b | lower}} import {{ b }}
+{% if b not in proto.message_names %}
 from core.models import {{ b }}
+{% endif %}
 {%- endif -%}
 {% endfor %}