Consolidate the IOV and non-IOV encryption/decryption code paths, and

Consolidate the IOV and non-IOV encryption/decryption code paths, and
drop the _iov suffix from most encryption- and decryption-related
functions.  The enc_provider encrypt and decrypt functions take IOVs,
as do the enctype entries in etypes.c, and there are no separate
encrypt_iov or decrypt_iov functions.

aead_provider is gone.  Enctype functions now take pointers to the
enctype entry instead of pointers to the enc/hash/aead providers; this
allows dk_encrypt and dk_decrypt to be polymorphic in the length
function they use now that AES and DES3 can't differentiate by aead
provider.

aes_string_to_key needed to be moved into the krb/ fold for this since
it's an enctype function; it was duplicated between builtin/ and
openssl/ before.  This leaves openssl/aes empty; the build system
currently demands that all modules have the same directory structure,
so the directory and Makefile will stick around for now.

Three separate copies of the derive_random logic are also now
consolidated into one.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@23444 dc483132-0cff-0310-8789-dd5450dbe970