Remove purpose checks in smime_keys.pl verify step.

Remove purpose checks in smime_keys.pl verify step.

The purpose checks are subsequently performed, and added as a field to
the .index.  In any case, it turns out passing multiple '-purpose'
arguments isn't even correct: openssl appears to just use the last
one.

Thanks to David J. Weller-Fahy for reporting the problem, and for
including a possible patch.