This was needed in the old days, where all the hotplug scripts did
nothing better than sleep for seconds to work around timing issues.
It made sure, that w continued to fork processes, while the machine
was doing nothing than sleeping, but the maximim number of childs
was already reached. This is no longer needed today, we do not run
many of these scripts anymore.
envp is not standardized, and may become invalid when environment variables
are modified. Since udev never actually uses it, we can simply remove it.
Should anyone miss it in future, they can use the standardized environ
variable - like udev_rules.c does already.
