This lets one avoid any decisions as to when to chdir there during its
execution and leads to better sandboxing because the pwd doesn't leak to
init() functions anymore.
Test: Manual.
Change-Id: I1560da8ed3a621249426f9e8908aa890c21e13ba
Also delete the now-unnecessary soong_env binary.
Test: Manually. Also checked what happens when a used environment
variable changes.
Change-Id: Ib393e7f444e94819198c6cce4bcd8719d9fd9441