if_wg: fix modules load on !x86

Only x86 provides optimized implementations via the blake2 module. The
software "reference" implementation is already included in the crypto(4)
module, we can drop the extra MODULE_DEPEND for other platforms.

Without this change, if_wg.ko could not be loaded due to the missing
dependency.

PR: 252156
Reported by: gbe
Sponsored by: The FreeBSD Foundation