don't set named curves explicitly in pre-3.0 libcrypto

don't set named curves explicitly in pre-3.0 libcrypto

The function `EC_KEY_set_asn1_flag` is deprecated in AWS-LC. Fortunately
calling it to make sure we use named curve keys is entirely unnecessary.

More information for pre-3.0 libcrypto and significant forks are as
following:

OpenSSL: Named curves were the default between 1.1.0 and 3.6.1 [1],[2]
AWS-LC: Library only supports named curves in the first place [3]
BoringSSL: Likewise with AWS-LC [4]
LibreSSL: `EC_GROUP`s are named by default [5]

[1] https://github.com/openssl/openssl/commit/86f300d38540ead85543aee0cb30c32145931744
[2] https://github.com/openssl/openssl/commit/9db6af922c48c5cab5398ef9f37e425e382f9440
[3] https://github.com/aws/aws-lc/blob/a605df416bc6ddd0a3b79d728770664ce2302e71/include/openssl/ec_key.h#L442-L445
[4] https://github.com/google/boringssl/blob/514abb73bb80130000b46cf589190c967c6647cd/include/openssl/ec_key.h#L279-L280
[5] https://github.com/libressl/openbsd/blob/c9338745181f31ae01336081edfdb738c0b76d5f/src/lib/libcrypto/ec/ec_lib.c#L94