Remove preferences upgrade from 2.1->2.2

No preferences will need to be upgraded.

Contributes to issue CURA-844.

plugins/VersionUpgrade/VersionUpgrade21to22/Preferences.py

@@ -1,20 +0,0 @@
-# Copyright (c) 2015 Ultimaker B.V.
-# Cura is released under the terms of the AGPLv3 or higher.
-
-##  Creates a new preferences instance by parsing a serialised preferences file
-#   in version 2 of the file format.
-#
-#   \param serialised The serialised form of a preferences file in version 2.
-#   \return A preferences instance, or None if the file format is incorrect.
-def importVersion2(serialised):
-    return None #Not implemented yet.
-
-##  A representation of a preferences file used as intermediary form for
-#   conversion from one format to the other.
-class Preferences:
-    ##  Serialises this preferences file as file format version 3.
-    #
-    #   \return A serialised form of this preferences file, serialised in
-    #   version 3 of the file format.
-    def exportVersion3():
-        raise Exception("Not implemented yet.")

plugins/VersionUpgrade/VersionUpgrade21to22/VersionUpgrade21to22.py

@@ -9,7 +9,7 @@ from . import Profile #To upgrade profiles.
 
 ##  Converts configuration from Cura 2.1's file formats to Cura 2.2's.
 #
-#   It converts the machine instances, preferences and profiles.
+#   It converts the machine instances and profiles.
 class VersionUpgrade21to22(VersionUpgrade):
     ##  Converts machine instances from format version 1 to version 2.
     #
@@ -22,17 +22,6 @@ class VersionUpgrade21to22(VersionUpgrade):
             return None
         return machine_instance.exportVersion2()
 
-    ##  Converts preferences from format version 2 to version 3.
-    #
-    #   \param serialised The serialised preferences file in version 2.
-    #   \return The serialised preferences file in version 3, or None if the
-    #   input was not of the correct format.
-    def upgradePreferences(self, serialised):
-        preferences = Preferences.importVersion2(serialised)
-        if not preferences: #Invalid file format.
-            return None
-        return preferences.exportVersion3()
-
     ##  Converts profiles from format version 1 to version 2.
     #
     #   \param serialised The serialised profile in version 1.

plugins/VersionUpgrade/VersionUpgrade21to22/__init__.py

@@ -20,10 +20,6 @@ def getMetaData():
                 "from": 1,
                 "to": 2
             },
-            "preferences": {
-                "from": 2,
-                "to": 3
-            },
             "machine_instance": {
                 "from": 1,
                 "to": 2