fix: use no icon theme as the default.

upstream: eclipse-theia/theia#12346
Signed-off-by: Akos Kitta <[email protected]>

Author: Akos Kitta

electron-app/package.json

@@ -39,6 +39,7 @@
           "light": "arduino-theme",
           "dark": "arduino-theme-dark"
         },
+        "defaultIconTheme": "none",
         "validatePreferencesSchema": false,
         "preferences": {
           "window.title": "${rootName}${activeEditorShort}${appName}",