parisc: Drop parisc special case for __sighandler_t

I believe we can and *should* drop this parisc-specific typedef for
__sighandler_t when compiling a 64-bit kernel. The reasons:

1. We don't have a 64-bit userspace yet, so nothing (on userspace side)
can break.

2. Inside the Linux kernel, this is only used in kernel/signal.c, in
function kernel_sigaction() where the signal handler is compared against
SIG_IGN.  SIG_IGN is defined as (__sighandler_t)1), so only the pointers
are compared.

3. Even when a 64-bit userspace gets added at some point, I think
__sighandler_t should be defined what it is: a function pointer struct.

I compiled kernel/signal.c with and without the patch, and the produced code
is identical in both cases.

Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Peter Collingbourne <pcc@google.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Reviewed-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/I21c43f21b264f339e3aa395626af838646f62d97
Link: https://lkml.kernel.org/r/a75b8eb7bb9eac1cf73fb119eb53e5892d6e9656.1605235762.git.pcc@google.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>