no-engine: fix signing with legacy app method based keys

no-engine: fix signing with legacy app method based keys

Signing with an app method based key (i.e. an `EVP_PKEY` which wraps an
`RSA` key with an application defined `RSA_METHOD`) used to work in 1.1.1.
That feature was broken in commit 60488d2434, but later on fixed by @t8m
in commit b247113c05 (see #14859).

This commit corrects a  minor flaw of the fix, which affects only
`no-engine` builds: the special treatment for foreign keys is guarded
by an `OPENSSL_NO_ENGINE` check.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from https://github.com/openssl/openssl/pull/22163)