Fix a possible memory leak in SM2 provider

Fix a possible memory leak in SM2 provider

ctx->propq that strdup from input parameter propq in sm2sig_newctx,
is not released. It should be released in sm2sig_freectx and copied
to dstctx in sm2sig_dupctx. And dstctx->id and dstctx->propq should
be set NULL to avoid releasing id/propq of srcctx when err occurs.

Signed-off-by: Huiyue Xu <xuhuiyue@huawei.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Yang <kaishen.yy@antfin.com>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22796)