crypto: fix rsa key gen with non-default exponent

EVP_PKEY_CTX_set_rsa_keygen_pubexp() accepts ownership of the exponent
on success, so do not free it.

Fixes: https://github.com/nodejs/node/issues/27087

PR-URL: https://github.com/nodejs/node/pull/27092


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>