[windows] Remove python2 specific hack

This PR ros#1872 made windows act differently than linux because of a specific python 2 delay doing unnecessary DNS checks for localhost.

The underlying code in python is different for python3 so the hack is no longer necessary. Given that, its better to reunify the codebase

tools/roslaunch/env-hooks/10.roslaunch.bat

@@ -1,15 +1,5 @@
 REM roslaunch/env-hooks/10.roslaunch.bat
 
-:: workaround Python 2 xmlrpc performance issue
-:: https://stackoverflow.com/questions/2617615/slow-python-http-server-on-localhost
-:: use IP address instead to avoid unnecessary DNS lookups.
 if "%ROS_MASTER_URI%" == "" (
-  set ROS_MASTER_URI=http://127.0.0.1:11311
-)
-
-:: it is discourage to set ROS_IP and ROS_HOSTNAME at the same time.
-if "%ROS_IP%" == "" (
-  if "%ROS_HOSTNAME%" == "" (
-    set ROS_IP=127.0.0.1
-  )
+  set ROS_MASTER_URI=http://localhost:11311
 )