Remove custom key length handling

Remove custom key length handling

No cipher in libcrypto is marked EVP_CIPH_CUSTOM_KEY_LENGTH and no control
handler deals with EVP_CTRL_SET_KEY_LENGTH, which means that this code is
dead as far as libcrypto is concerned. Almost nothing uses EVP_CIPHER_meth*
(this was added for a single project) and nothing sets a custom ctrl. This
isn't going to change anyway since EVP_CIPHER_meth* is deprecated in order
to promote more provider beauty.

ok beck jsing