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 https://lab.nexedi.com/nexedi/slapos/merge_requests/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