Revert "Fix gcode.gz double extension problem on Mac"

This reverts commit fa90fcf18e.

CURA-5228

plugins/GCodeGzReader/GCodeGzReader.py

@@ -3,11 +3,11 @@
 
 import gzip
 
-from UM.Platform import Platform
+from io import TextIOWrapper
+
 from UM.Mesh.MeshReader import MeshReader #The class we're extending/implementing.
 from UM.PluginRegistry import PluginRegistry
 
-
 ##  A file reader that reads gzipped g-code.
 #
 #   If you're zipping g-code, you might as well use gzip!
@@ -15,7 +15,7 @@ class GCodeGzReader(MeshReader):
 
     def __init__(self):
         super().__init__()
-        self._supported_extensions = [".gz"]
+        self._supported_extensions = [".gcode.gz"]
 
     def read(self, file_name):
         with open(file_name, "rb") as file: