CURA-5128 cleanup .gz and only leave .gcode.gz as Cura and Uranium now accept extensions with multiple periods

plugins/GCodeGzReader/__init__.py

@@ -18,5 +18,4 @@ def getMetaData():
 
 def register(app):
     app.addNonSliceableExtension(".gcode.gz")
-    app.addNonSliceableExtension(".gz")  # in some parts only the last extension is taken. Let's make it a non sliceable extension for now
     return { "mesh_reader": GCodeGzReader.GCodeGzReader() }