core: drop Base_uniqueReferenceInFolderValidator

We use AttributeUnicityConstraint for this kind of checks nowadays.

Also the way "context document" was accessed does not work in RenderJS
UI

product/ERP5/bootstrap/erp5_core/SkinTemplateItem/portal_skins/erp5_core/Base_uniqueReferenceInFolderValidator.py

-"""Check the object have an unique reference in it's parent folder
-"""
-from Products.ERP5Type.Log import log
-if editor is None : 
-  return 1
-
-reference = editor
-
-document = context.restrictedTraverse(request.object_path, None)
-if document is None : 
-  log('Base_uniqueReferenceInFolderValidator', 'document is None')
-  return 0
-
-parent_folder = document.getParentValue()
-for same_reference in parent_folder.searchFolder(reference = reference):
-  if same_reference.uid != document.getUid() :
-    log('Base_uniqueReferenceInFolderValidator',
-                        'another document with reference %s exists at %s' % (reference, same_reference.getPath()))
-    return 0
-
-return 1

product/ERP5/bootstrap/erp5_core/SkinTemplateItem/portal_skins/erp5_core/Base_uniqueReferenceInFolderValidator.xml

-<?xml version="1.0"?>
-<ZopeData>
-  <record id="1" aka="AAAAAAAAAAE=">
-    <pickle>
-      <global name="PythonScript" module="Products.PythonScripts.PythonScript"/>
-    </pickle>
-    <pickle>
-      <dictionary>
-        <item>
-            <key> <string>Script_magic</string> </key>
-            <value> <int>3</int> </value>
-        </item>
-        <item>
-            <key> <string>_bind_names</string> </key>
-            <value>
-              <object>
-                <klass>
-                  <global name="NameAssignments" module="Shared.DC.Scripts.Bindings"/>
-                </klass>
-                <tuple/>
-                <state>
-                  <dictionary>
-                    <item>
-                        <key> <string>_asgns</string> </key>
-                        <value>
-                          <dictionary>
-                            <item>
-                                <key> <string>name_container</string> </key>
-                                <value> <string>container</string> </value>
-                            </item>
-                            <item>
-                                <key> <string>name_context</string> </key>
-                                <value> <string>context</string> </value>
-                            </item>
-                            <item>
-                                <key> <string>name_m_self</string> </key>
-                                <value> <string>script</string> </value>
-                            </item>
-                            <item>
-                                <key> <string>name_subpath</string> </key>
-                                <value> <string>traverse_subpath</string> </value>
-                            </item>
-                          </dictionary>
-                        </value>
-                    </item>
-                  </dictionary>
-                </state>
-              </object>
-            </value>
-        </item>
-        <item>
-            <key> <string>_params</string> </key>
-            <value> <string>editor, request</string> </value>
-        </item>
-        <item>
-            <key> <string>id</string> </key>
-            <value> <string>Base_uniqueReferenceInFolderValidator</string> </value>
-        </item>
-      </dictionary>
-    </pickle>
-  </record>
-</ZopeData>