BUG/MINOR: mux-quic: ignore remote unidirectional stream close

BUG/MINOR: mux-quic: ignore remote unidirectional stream close

Remove ABORT_NOW() on remote unidirectional stream closure. This is
required to ensure our implementation is evolutive enough to not fail on
unknown stream type.

Note that for the moment MAX_STREAMS_UNI flow-control frame is never
emitted. This should be unnecessary for HTTP/3 which have a limited
usage of unidirectional streams but may be required if other application
protocols are supported in the future.

ABORT_NOW() was triggered by s2n-quic which opens an unknown
unidirectional stream with greasing. This was detected by QUIC interop
runner for http3 testcase.

This must be backported up to 2.6.