Revert "Do not set ro.iorapd.enable=true"

This reverts commit 4a4a4df0.

Reason for revert: This CL leaves the flag unset. Iorap is disabled by default now and rely on this flag to wake up in Rasta experiment.

IORap is disabled by default. We set this flag to run
Rasta experiment. This conflicts with go/aog/1557011.

To be more specific about how "ro.iorapd.enable" works now,
we added two device configs.
Iorap by default is off and starts when
(https://source.corp.google.com/android/system/iorap/iorapd.rc?q=iorapd.rc)

* ro.iorapd.enable is true excluding unset
* One of the device configs is true.

We have to set "ro.iorapd.enable" to true, so that iorap
can be started in the Rasta experiments.

Change-Id: I9630712b74cd411a5678632fb1ff695a84ed1048