Revert "[libc++] Integrate the PSTL into libc++"

This reverts r366593, which caused unforeseen breakage on the build bots.
I'm reverting until the problems have been figured out and fixed.

llvm-svn: 366603
GitOrigin-RevId: a3c83b7511a56a1bc79784078caab0ad7f8c7abb
1 file changed