Tom,
You can browse for the widgets original icon in the widgets folder of that app or the easier way is to open the main config.json in the apps root folder and find the widget(s) in question and delete the icon line.
Before:
{
"position": {
"left": 105,
"top": 45,
"relativeTo": "map"
},
"placeholderIndex": 1,
"id": "_7",
"name": "Edit",
"version": "2.9",
"closeable": true,
"uri": "widgets/Edit/Widget",
"config": "configs/Edit/config__7.json",
"icon": "configs\\Edit\\icon__7.png"
},
After:
{
"position": {
"left": 105,
"top": 45,
"relativeTo": "map"
},
"placeholderIndex": 1,
"id": "_7",
"name": "Edit",
"version": "2.9",
"closeable": true,
"uri": "widgets/Edit/Widget",
"config": "configs/Edit/config__7.json"
},