vquic: drop support for OpenSSL-QUIC

vquic: drop support for OpenSSL-QUIC

- It is slower and uses more memory than the alternatives and is only
  experimental in curl.
- We disable a few tests for OpenSSL-QUIC because of flakiness
- It gets little attention from OpenSSL and we have no expectation of the
  major flaws getting corrected anytime soon.
- No one has spoken up for keeping it
- curl users building with vanilla OpenSSL can still use QUIC through the
  means of ngtcp2

Closes #20226