Fix location of slash

As Sam Harwell noticed, the slash should be outside of the parameter
tags for /fw/firewall_policies/firewall_policy-id/remove_rule.

This is a followup to change I174f5d6ca5291bff88c1b8350b48f5d97daf4c34.

Change-Id: I5f30b4d2ac65efff604ee5e424060805e7cf30e5
Related-Bug: #1265927
Merge "Fix location of slash"