Remove legacy sign/verify from EVP_MD.

Remove sign/verify and required_pkey_type fields of EVP_MD: these are a
legacy from when digests were linked to public key types. All signing is
now handled by the corresponding EVP_PKEY_METHOD.

Only allow supported digest types in RSA EVP_PKEY_METHOD: other algorithms
already block unsupported types.

Remove now obsolete EVP_dss1() and EVP_ecdsa().

Reviewed-by: Richard Levitte <levitte@openssl.org>

engines/e_dasync.c

@@ -94,13 +94,12 @@ static const EVP_MD dasync_sha1 = {
     NID_sha1,
     NID_sha1WithRSAEncryption,
     SHA_DIGEST_LENGTH,
-    EVP_MD_FLAG_PKEY_METHOD_SIGNATURE | EVP_MD_FLAG_DIGALGID_ABSENT,
+    EVP_MD_FLAG_DIGALGID_ABSENT,
     dasync_sha1_init,
     dasync_sha1_update,
     dasync_sha1_final,
     NULL,
     NULL,
-    EVP_PKEY_NULL_method,
     SHA_CBLOCK,
     sizeof(EVP_MD *) + sizeof(SHA_CTX),
 };