freebsd32: remove redundant no-arg syscalls

pipe requires no special handling.

ofreebsd32_sigpending did differ from osigpending in that it acted
on the siglist rather than the sigqueue, but this appears to be an
oversight in 3fbdb3c21524d9d95278ada1d61b4d1e6bee654b.

ogetpagesize could theoretically have ABI-dependent results, but in
practice does not. If it does it would be easy handle in the central
implementation and be the least of the problems in changing the value of
PAGE_SIZE.

Reviewed by: kevans