* src/channel.c (register_channel): Deleted connection argument.

* src/channel.h (ssh_channel): Replaced the write pointer with a
pointer to the connection.
(channel_request): Deleted connection argument.
* src/channel.h (CHANNEL_REQUEST): Likewise.

Rev: src/channel.c:1.103
Rev: src/channel.h:1.69
Rev: src/channel_commands.c:1.25
Rev: src/client_pty.c:1.19
Rev: src/gateway_channel.c:1.10
Rev: src/server_session.c:1.66
Rev: src/tcpforward_commands.c:1.35