Memory leak in AES_crypt

This is in svn rev 724, and many earlier.

AES_crypt does not free its output buffer, leaking it on every use.

Given that _aes.i is mostly not exposed through the Python
objects, and the interface is obsolete in favor of EVP, this
probably impacts very few applications.

https://bugzilla.osafoundation.org/show_bug.cgi?id=12999