Remove some PR_SET_VMAs during pthread_create

PR_SET_VMA takes mmap_sem, which can cause contention and reduce
performance any time many threads are created at the same time,
like app startup.

Test: camera launch performance
Bug: 122471935
Change-Id: If7fa7ad99654c01d503f694976fd92bfd30d2afd
Merged-in: If7fa7ad99654c01d503f694976fd92bfd30d2afd