Bug 1266999 - Stop writing XPT_NAME in backend.mk; r=glandium

It is unused and no longer serves a purpose.

MozReview-Commit-ID: ECzfSbqgA1z

--HG--
extra : rebase_source : 0e0104b42a73c2436b59f09732c27e78a2619ca1

python/mozbuild/mozbuild/backend/recursivemake.py

@@ -229,8 +229,6 @@ class BackendMakeFile(object):
 
     def close(self):
         if self.xpt_name:
-            self.fh.write('XPT_NAME := %s\n' % self.xpt_name)
-
             # We just recompile all xpidls because it's easier and less error
             # prone.
             self.fh.write('NONRECURSIVE_TARGETS += export\n')