Remove PK_PKCS1_PADDING
Right now, nothing uses the PK_PKCS1_PADDING value. And a good thing too, since it's completely wrong for encryption, and the stuff that does signing already uses it, hardwired.
To avoid regrettable accidents in the future, we should remove PK_PKCS1 from crypto.h, and make (most?) stuff that used to support it, not.