BaseTools: UPT/Xml: Remove unnecessary code

Running the vulture tool on the UPT/Xml folder gave the following
report. Remove the unnecessary code.

- UPT/Xml/CommonXml.py:585:
  unused attribute 'LangDefsList' (60% confidence)

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>

BaseTools/Source/Python/UPT/Xml/CommonXml.py

@@ -582,7 +582,6 @@ class UserExtensionsXml(object):
         self.BinaryDescriptionList = []
         self.BinaryCopyrightList = []
         self.BinaryLicenseList = []
-        self.LangDefsList = []
         self.DefineDict = {}
         self.BuildOptionDict = {}
         self.IncludesDict = {}