Remove unused 32-bit compatibility structures from cryptodev.

The counters are exported by a sysctl and have the same width on all
platforms anyway.

Reviewed by: cem, delphij, jhb
Sponsored by: Rubicon Communications, LLC (Netgate)
Differential Revision: https://reviews.freebsd.org/D25465

(cherry picked from commit a5ae70f5a0554235c499016bec3a721adbb1043a)