Revert part of r294418 ("Correct ranges...")

Commit was temporary fix due to rman_res_t defined as 32-bit u_long.
After redefining it as 64-bit variable workaround is not needed and
was removed.

Submitted by: Bartosz Szczepanek <bsz@semihalf.com>
Obtained from: Semihalf
Sponsored by: Stormshield
Differential revision: https://reviews.freebsd.org/D6214