Revert "devstack: Fix neutron configuration to run in OSIC"

This reverts commit 45f071e36e.

The Temporary fix can be reverted as devstack has released
the fix in following patch:-
https://review.openstack.org/398012

Change-Id: I837f4925cf4c797bd1b02a7bf244ca5742159971
Closes-Bug: #1628267
Closes-Bug: #1629133

devstack/settings

@@ -5,9 +5,6 @@
 # PUBLIC_NETWORK_GATEWAY=192.168.1.225
 # PUBLIC_INTERFACE=em1
 # FIXED_RANGE=10.0.0.0/24
-# FIXME: Add FIXED_RANGE until devstack/neutron is fixed globally
-SUBNETPOOL_PREFIX_V4=$FIXED_RANGE
-
 ## Log all output to files
 # LOGFILE=$HOME/devstack.log
 # SCREEN_LOGDIR=$HOME/logs