This is a rebase of the patch from [0]. It removes the internal padding
implementation in pgcrypto and lets OpenSSL do it. The internal
implementation was once applicable to the non-OpenSSL code paths, but
those have since been removed.
[0]:
https://www.postgresql.org/message-id/b1a62889-bb45-e5e0-d138-7a370a0a334f@enterprisedb.com