property_sheets: drop Item.package_type

This category never existed and this is always logging:

    Base Category 'package_type' is missing. Accessors can not be generated.

product/ERP5/bootstrap/erp5_property_sheets/PropertySheetTemplateItem/portal_property_sheets/Item/package_type_category.xml

-<?xml version="1.0"?>
-<ZopeData>
-  <record id="1" aka="AAAAAAAAAAE=">
-    <pickle>
-      <global name="Category Property" module="erp5.portal_type"/>
-    </pickle>
-    <pickle>
-      <dictionary>
-        <item>
-            <key> <string>id</string> </key>
-            <value> <string>package_type_category</string> </value>
-        </item>
-        <item>
-            <key> <string>portal_type</string> </key>
-            <value> <string>Category Property</string> </value>
-        </item>
-      </dictionary>
-    </pickle>
-  </record>
-</ZopeData>