Remove old fork-and-specialize API

As promised, this is the cleanup patch-set which removes the
old native "fork and specialize" API, which has been replaced
by a slightly-enhanced one which can close the Zygote socket
descriptors in the Zygote child.

Change-Id: I096f058e851aa079e342ecc718ff5757db68c8cd

Patchset: 1
http://review.cyanogenmod.org/#/c/60044/
(cherry picked from commit 30859608c50b90ba453adafe5021f95cd065bf7d)