Stop setting swappiness.

We're re-enabling memory cgroups on Ariel
to use user-space lmkd. As a side-effect, this
code will start setting swappiness again. Since the
benefit of swappiness is unknown at this point
(see b/18248535 for details), disable it until
we have good data it helps.

Change-Id: I8e8b892ba0db27469f2d47615f71ce1d2712acbf