CORE: Do a bit of cleanup of core fetching

CORE: Do a bit of cleanup of core fetching

Some data, like the library context, were passed both through higher
level callback structures and through arguments to those same higher
level callbacks.  This is a bit unnecessary, so we rearrange the
callback arguments to simply pass that callback structure and rely on
the higher level fetching functionality to pick out what data they
need from that structure.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15750)