Remove the _fetch_by_number functions

Remove the _fetch_by_number functions

These functions are unused and untested.  They are also implemented rather
inefficiently.  If we ever needed them in the future, they'd almost surely
need to be rewritten more efficiently.

Fixes #18227

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18237)