Remove unused function prototypes

`args_verify()` and `opt_reset()` are declared in `apps/apps.h`, but they are
not referenced anywhere. So can we remove them from `apps.h`?

Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3995)