[PATCH 0 of 4] QUIC cleanup

[Roman Arutyunyan]

- The first patch removes QUIC from Stream.

- After removing QUIC from Stream, the only thing left in Stream diff is
  UDP-specific rbtree initialization.  After splitting UDP and QUIC
  implementations, rbtrees are now initialized separately.  The second patch
  brings back single initialization.  This is an optional non-cleanup patch.

- The third patch removes server push from HTTP/3.

- The fourth patch removes README.