Drop "by store"'s by_store_subject_ex()

Drop "by store"'s by_store_subject_ex()

It was used to pass libctx and propq, which would override the
corresponding values passed to by_store_ctrl_ex().  This wasn't
really reasonable to do either way, as it could potentially be a
surprise to the user, who can reasonably expect that the URI is
opened with the libctx and propq that was passed with the URI, and
not with those passed later.

Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27529)