opam, tcpcl: drop dead helpers
- ocaml-opam/lib/lexer.ml: remove unused [peek_int] and [is_eof].
[peek_char] is the only peeker the parser uses; the others were
written speculatively and never wired in.
- ocaml-tcpcl/lib/tcpcl.ml: remove unused [V3.refuse_reason_typ]
uint8 codec. V3 packs the refuse reason into the message header
flags nibble (encode_msg_hdr ~flags:(refuse_reason_to_int r)),
so the standalone uint8 codec was never reached.