acct: encode_comp_t(0) is 0, fortunately...

There was an amusing bogosity in ac_rw calculation - it tried to
do encode_comp_t(encode_comp_t(0) / 1024).  Seeing that comp_t is
a 3-bit exponent + 13-bit mantissa... it's a good thing that 0 is
represented by all-bits-clear.

The history of that one is interesting - it was introduced in
2.1.68pre1, when acct.c had been reworked and moved to separate
file.  Two months later (2.1.86) somebody has noticed that the
sucker won't compile - there was no task_struct::io_usage.
At which point the ac_io calculation had changed from
encode_comp_t(current->io_usage) to encode_comp_t(0) and the
bug in the next line (absolutely real back then, had it ever
managed to compile) become a harmless bogosity.  Looks like
nobody has ever noticed until now.

Anyway, let's bury that idiocy now that it got noticed.  17 years
is long enough...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/acct.c

@@ -531,9 +531,6 @@ static void do_acct_process(struct bsd_acct_struct *acct,
 	ac.ac_majflt = encode_comp_t(pacct->ac_majflt);
 	ac.ac_exitcode = pacct->ac_exitcode;
 	spin_unlock_irq(&current->sighand->siglock);
-	ac.ac_io = encode_comp_t(0 /* current->io_usage */);	/* %% */
-	ac.ac_rw = encode_comp_t(ac.ac_io / 1024);
-	ac.ac_swaps = encode_comp_t(0);
 
 	/*
 	 * Get freeze protection. If the fs is frozen, just skip the write