Comment out opr_AssertionFailed from afsrpc.def

Comment out opr_AssertionFailed from afsrpc.def

Apparently the Windows utilities link opr.lib directly, so this
caused a "multiply defined symbol" error.

Reviewed-on: https://gerrit.openafs.org/13216
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 907e09ff2b7e86005765a594db27e1df194ec204)

Change-Id: Ibdd1388235086177bd3fec3c1088916d71fc204f
Reviewed-on: https://gerrit.openafs.org/13221
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>