Remove pre-existing assert macro in hcrypto header.

Remove pre-existing assert macro in hcrypto header.

The config.h header for hcrypto defines an assert macro for
use by RX. OpenBSD already has an assert macro definition so
this new one causes screaming by the compiler about
re-definition. This patch adds the directives to remove any
pre-existing definition of assert, if one exists, prior to
defining the new one.

Change-Id: I01d5a1f26617fecfd0ffcc3930a7c7881beb8183
Reviewed-on: http://gerrit.openafs.org/4958
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>