VR services: don't writepid to /dev/cpuset/tasks

Currently bufferhubd and performanced's pid gets written into
/dev/cpuset/tasks. When start them on systems without cpuset support, it
will cause the creation of /dev/cpuset/tasks file by accident and
confuses Android system that cpuset is actually supported. Actually,
there is no need to explicitly put the service in the root cpuset, it
goes there by default if cpuset is supported.

Bug: 69057609
Bug: 64377040
Test: Build and boot system
Change-Id: Ia53345869fb5381b0e51e48ef6c7b85ddcfcafa1