Remove redundant type check in set_default_branch

The passed `name` parameter is always of type `str` in Python 3
hence the type check is redundant and no longer needed.

hg2git.py

@@ -23,7 +23,7 @@ user_clean_re=re.compile(b'^["]([^"]+)["]$')
 
 def set_default_branch(name):
   global cfg_master
-  cfg_master = name.encode('utf8') if not isinstance(name, bytes) else name
+  cfg_master = name.encode('utf8')
 
 def set_origin_name(name):
   global origin_name