engines/http: silence openssl 3.0 deprecation warnings

engines/http: silence openssl 3.0 deprecation warnings

Maybe someone will fix these one day, for now shut up the annoying
warning about certain functions being deprecated. Example:

engines/http.c: In function ‘_gen_hex_md5’:
engines/http.c:261:9: warning: ‘MD5’ is deprecated: Since OpenSSL 3.0 [-Wdeprecated-declarations]
  261 |         MD5((unsigned char*)p, len, hash);
      |         ^~~
In file included from engines/http.c:28:
/usr/include/openssl/md5.h:52:38: note: declared here
   52 | OSSL_DEPRECATEDIN_3_0 unsigned char *MD5(const unsigned char *d, size_t n,
      |                                      ^~~
engines/http.c: In function ‘_hmac’:
engines/http.c:273:9: warning: ‘HMAC_CTX_new’ is deprecated: Since OpenSSL 3.0 [-Wdeprecated-declarations]
  273 |         ctx = HMAC_CTX_new();
      |         ^~~

Signed-off-by: Jens Axboe <axboe@kernel.dk>