Revert "Extension prefix in BusinessTemplate was added twice."

This reverts commit deb7e37e7690d50a6dc1e9aab05f4a7099973287 which introduced
a regression (test_BusinessTemplateWithDocumentPropertySheetMigrated failed).

Conflicts:

	product/ERP5/Document/BusinessTemplate.py

product/ERP5/Document/BusinessTemplate.py

@@ -3538,6 +3538,15 @@ class FilesystemToZodbTemplateItem(FilesystemDocumentTemplateItem,
         result = getattr(FilesystemDocumentTemplateItem,
                          method_name)(self, *args, **kw)
 
+      if method_name == 'preinstall':
+        old_result = result.copy()
+        for k, v in old_result.iteritems():
+          if not k.startswith(self._tool_id + '/'):
+            result.pop(k)
+            # Magical way to have unique path in case of not yet migrated property
+            # sheets available on preinstall list
+            k = self._getKey(k)
+          result[k] = v
       return result
     return inner