Long time ago I installed this plugin to easily add urls to tiddlers in edit mode.
It turns out I never use it and would like to remove it. But I can’t find how! It isn’t listed in the plugins tab of Control Panel nor in tiddlywiki.info and I have no “plugins” directory in the path served by node.js.
I searched the web trying to find where it came from without success… 
Someone could give me clue?
Thank you.
This happened to me a couple of times with other plugins that introduce editor toolbar buttons.
I’m not sure exactly, but I presume when you edit the button, you make it a shadow of the original button from the plugin. When you remove the plugin, the shadow will not be removed.
To get rid of it, look through all editor toolbar buttons. Go to Advanced Search → Filter tab → put in filter
[all[tiddlers+shadows]tag[$:/tags/EditorToolbar]!prefix[$:/core/ui/EditorToolbar]]
These are editor toolbar buttons that do not come from TW core, that is they come from plugins, unless you added some yourself. See if you find the leftover drag and drop button and delete it.
Alternatively, you can go to sidebar → More → Explorer and browse the plugins folder, see if there are any leftovers of the plugin.
Right on!
The culprit was “URL Import Gadget” and your filter made me find it immediately.
Thank you Vilc.