QUIC: removed compatibility with older BoringSSL API.

QUIC: removed compatibility with older BoringSSL API.

SSL_CIPHER_get_protocol_id() appeared in BoringSSL somewhere between
BORINGSSL_API_VERSION 12 and 13 for compatibility with OpenSSL 1.1.1.
It was adopted without a proper macro test, which remained unnoticed.
This justifies that such old BoringSSL API isn't widely used and its
support can be dropped.

While here, removed SSL_set_quic_use_legacy_codepoint() that became
useless after the default was flipped in BoringSSL over a year ago.