Get rid of the postrandom script.  It was born in a time when the
random script ran before filesystems were mounted, which is no
longer the case.

In random_start(), immediately delete each file that is fed into
/dev/random, and recreate the default entropy file immediately
after reading and deleting it.  The logic used in random_stop()
to determine which file to write to should probably be factored
out and used here as well.
Restore the auto-reseed logic, but move it to a much later point,
immediately before kick_init.

Approved by:	so (self)