7646: [Unit test] typo on 'gramps.gen.utils.file.py'

Replace the call with ensuring that dirname is unicode; since
TMP_DIR is guaranteed to be, os.path.join() willl return a unicode so
further conversion is unnecessary.

(cherry picked from commit 4327f6952b)

gramps/gen/utils/file.py

@@ -95,11 +95,10 @@ def get_empty_tempdir(dirname):
     or for inadequate permissions to delete dir/files or create dir(s)
 
     """
-    dirpath = os.path.join(TEMP_DIR,dirname)
+    dirpath = os.path.join(TEMP_DIR,cuni(dirname))
     if os.path.isdir(dirpath):
         shutil.rmtree(dirpath)
     os.makedirs(dirpath)
-    dirpath = get_unicode_path_from_env_var(dirpath)
     return dirpath
 
 def rm_tempdir(path):