Remove the old buffer management code

Remove the old buffer management code

We no longer use the old buffer management code now that it has all been
moved to the new record layer.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19424)