ssh/terminal: use console functions, types and consts from x/sys/windows
ssh/terminal: use console functions, types and consts from x/sys/windows

Use GetConsoleMode, SetConsoleMode and GetConsoleScreenBufferInfo and
the corresponding types and constants from golang.org/x/sys/windows
instead of locally defining them.

Change-Id: I69292a47114d071be261ffda6ca620a0b9820d00
Reviewed-on: https://go-review.googlesource.com/52990
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Alex Brainman <54ba58c8441b5eff861de6b4e5ee46baf086b142@gmail.com>

ScriptRock/crypto,golang/crypto,golang/crypto,ScriptRock/crypto,golang/crypto