Remove support for geli(4) algorithms deprecated in r348206.

This removes support for reading and writing volumes using the
following algorithms:

• Triple DES
• Blowfish
• MD5 HMAC integrity

In addition, this commit adds an explicit whitelist of supported
algorithms to give a better error message when an invalid or
unsupported algorithm is used by an existing volume.

Reviewed by: cem
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D24343