forge: do not link to Bug portal_type base categories that are already...

forge: do not link to Bug portal_type base categories that are already provided by Bug property_sheet

bt5/erp5_forge/PortalTypeBaseCategoryTemplateItem/base_category_list.xml

 <base_category_list>
  <portal_type id="Bug">
   <item>aggregate</item>
-  <item>bug_difficulty</item>
-  <item>bug_priority</item>
-  <item>bug_severity</item>
  </portal_type>
  <portal_type id="Bug Module">
   <item>business_application</item>

bt5/erp5_forge/bt/template_portal_type_base_category_list

 Bug Module | business_application
 Bug | aggregate
-Bug | bug_difficulty
-Bug | bug_priority
-Bug | bug_severity
 Glossary Module | business_application
 Glossary Term | business_field
 Glossary Term | causality
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