Remove sslkeylog file setup from quic-hq-interop

Remove sslkeylog file setup from quic-hq-interop

Now that libcrypto supports the user of SSLKEYLOGFILE, the interop demo
attempts to open the same file based on the same env variable.

The hq-interop-demo code can just be removed, and it fixes the open
failure when both libcrypto and hq-interop attempt to open and write the
same file, which is causing the nightly failure

Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25819)