Removes the '.desktop' suffix from the
`QGuiApplication.setDesktopFileName` argument to prevent the following
warning on startup of Electrum:
```
QGuiApplication::setDesktopFileName: the specified desktop file name ends with .desktop.
For compatibility reasons, the .desktop suffix will be removed.
Please specify a desktop file name without .desktop suffix
```
The [qt
docs](https://doc.qt.io/qtforpython-6/PySide6/QtGui/QGuiApplication.html#PySide6.QtGui.QGuiApplication.desktopFileName)
say that `desktopFileName` is "... is the file name, without the full
path or the trailing “.desktop” extension of the desktop entry that
represents this application according to the freedesktop desktop entry
specification."
c7e3fec69e