Remove support for AES-based DNS cookies and AES implementation

The legacy support for AES-based DNS cookies should go, which will resolve following:

The functions isc_aes256_crypt() and isc_aes192_crypt() in lib/isc/aes.c have no callers besides test code and should be removed.

as we are going to remove the AES implementation in libisc completely.

Edited Nov 07, 2023 by Ondřej Surý

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