Remove python 2 specific code after NB port

Author: kevin-bates

jupyter_server/base/handlers.py

@@ -26,7 +26,7 @@
 
 from traitlets.config import Application
 from ipython_genutils.path import filefind
-from ipython_genutils.py3compat import string_types, PY3
+from ipython_genutils.py3compat import string_types
 
 import jupyter_server
 from jupyter_server._tz import utcnow
@@ -405,10 +405,6 @@ def check_host(self):
         if host.startswith('[') and host.endswith(']'):
             host = host[1:-1]
 
-        if not PY3:
-            # ip_address only accepts unicode on Python 2
-            host = host.decode('utf8', 'replace')
-
         try:
             addr = ipaddress.ip_address(host)
         except ValueError: