MINOR: quic: Remove pool_head_quic_be_cc_buf pool

MINOR: quic: Remove pool_head_quic_be_cc_buf pool

This patch impacts the QUIC frontends. It reverts this patch

    MINOR: quic-be: add a "CC connection" backend TX buffer pool

which adds <pool_head_quic_be_cc_buf> new pool to allocate CC (connection closed state)
TX buffers with bigger object size than the one for <pool_head_quic_cc_buf>.
Indeed the QUIC backends must be able to send at least 1200 bytes Initial packets.

For now on, both the QUIC frontends and backend use the same pool with
MAX(QUIC_INITIAL_IPV6_MTU, QUIC_INITIAL_IPV4_MTU)(1252 bytes) as object size.