Never use des_set_key (it depends on the global variable des_check_key),
but usually des_set_key_unchecked.
Only destest.c bothered to look at the return values of des_set_key,
but it did not set des_check_key -- if it had done so,
most checks would have failed because of wrong parity and
because of weak keys.

and delete an unused file.

Allow configuring the name of that header file.

Submitted by: Richard Levitte <richard@levitte.org>

Submitted by:
Reviewed by:
PR: