Install Guide: Remove redundant RHEL instructions

Step 3 and 4 both contained the same lines on setup of qpid,
remove it from step 3.

Change-Id: I55ae2279f95ab7f4bd65c08b43153dbedc3fb4b4
backport: havana
Closes-Bug: 1254871
(cherry picked from commit 3e943333ee9fc3e6176610112ddeb66d141a24ec)