erp5_advanced_trade: delete script `Movement_isQuantityEditable`

The script now has a drop-in replacement in `erp5_trade` which works as-is even
in the case of advanced trade (calls `Movement_isQuantityEnabled`). Henceforth,
the custom script in `erp5_advanced_trade` is not needed anymore.

bt5/erp5_advanced_trade/SkinTemplateItem/portal_skins/erp5_advanced_trade/Movement_isQuantityEditable.py

-"""This script is used to know if quantity can be edited by user.
-
-* If this is not a movement (line containing lines or cell), user
-cannot edit this line which is just a container, but no actual movement.
-
-* If items are used, quantity is set by the item quantity.
-"""
-
-if not context.isMovement():
-  return False
-
-return not (context.getResource() and context.getResourceValue().getAggregatedPortalTypeList())

bt5/erp5_advanced_trade/SkinTemplateItem/portal_skins/erp5_advanced_trade/Movement_isQuantityEditable.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>_bind_names</string> </key>
-            <value>
-              <object>
-                <klass>
-                  <global name="_reconstructor" module="copy_reg"/>
-                </klass>
-                <tuple>
-                  <global name="NameAssignments" module="Shared.DC.Scripts.Bindings"/>
-                  <global name="object" module="__builtin__"/>
-                  <none/>
-                </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></string> </value>
-        </item>
-        <item>
-            <key> <string>id</string> </key>
-            <value> <string>Movement_isQuantityEditable</string> </value>
-        </item>
-      </dictionary>
-    </pickle>
-  </record>
-</ZopeData>