monaco_editor: use default multiCursorModifier

This was a workaround for ChromeOS, but we realized it was not really good.
Disable it for the same reasons as nexedi/slapos!1196 :

 - not everybody use ChromeOS
 - this breaks the ctrl+click shortcut to go to definition/follow link
 - it makes ERP5 monaco editor behaves differently from others monaco editor
 - ChromeOS users can use chrome://flags/#use-search-click-for-right-click

bt5/erp5_monaco_editor/SkinTemplateItem/portal_skins/erp5_monaco_editor/monaco-editor.gadget.js.js

@@ -29,8 +29,6 @@
       context.editor = editor = monaco.editor.create(
         this.element.querySelector('.monaco-container'),
         {
-          /* because Alt+Click is LeftClick on ChromeOS */
-          multiCursorModifier: 'ctrlCmd',
           autoIndent: true,
           automaticLayout: true,
         }

bt5/erp5_monaco_editor/SkinTemplateItem/portal_skins/erp5_monaco_editor/monaco_editor_support.zpt

@@ -103,10 +103,6 @@ $script.onload = function() {
     {
       value: $textarea.value,
       language: mode,
-
-      /* because Alt+Click is LeftClick on ChromeOS */
-      multiCursorModifier: "ctrlCmd",
-
       autoIndent: true
     }
   );