src/fssum: use newer EVP_* interface to replace deprecated MD5_* interace

src/fssum: use newer EVP_* interface to replace deprecated MD5_* interace

In OpenSSL 3.0, MD_Init/Update/Final() interfaces are marked
deprecated, and we have to go EVP_DigestInit/Update/Final() instead.

Personally I'm not a fan of this, especially the new EVP_MD_CTX
structure can no longer be stack allocated, thus we have to
dynamically allocate and free EVP_MD_CTX in sum_init() and sum_free().

Hopes this is proper way to go and would solve the problem until
OpenSSL chooses to change their interface again.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>