Replace BUF_ string function calls with OPENSSL_ ones

Replace BUF_ string function calls with OPENSSL_ ones

Deprecate the BUF_ string macros

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10207)