Don't attempt to deactive child providers if we don't need to

Don't attempt to deactive child providers if we don't need to

If a provider doesn't have any child providers then there is no need
to attempt to remove them - so we should not do so. This removes some
potentialy thread races.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16980)