Do not disable sig-proxy when using a TTY

This partially reverts https://github.com/moby/moby/commit/e0b59ab52b87b8fc15dd5534c3231fdd74843f9f,
and does not automatically disable proxying signals in TTY-mode

Before this change:
------------------------------------

Start a container with a TTY in one shell:

```
docker run -it --init --name repro-28872 busybox sleep 30
```

then, in another shell, kill the docker cli:

```
kill `pgrep -f repro-28872`
```

Notice that the CLI was killed, but the signal not forwarded to the container;
the container continues running

```
docker container inspect --format '{{ .State.Status }}' repro-28872
running

docker container rm -f repro-28872
```

After this change:
------------------------------------

Start a container with a TTY in one shell:

```
docker run -it --init --name repro-28872 busybox sleep 30
```

then, in another shell, kill the docker cli:

```
kill `pgrep -f repro-28872`
```

Verify that the signal was forwarded to the container, and the container exited

```
docker container inspect --format '{{ .State.Status }}' repro-28872
exited

docker container rm -f repro-28872
```

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/container/run.go

@@ -117,11 +117,6 @@ func runContainer(dockerCli command.Cli, opts *runOptions, copts *containerOptio
 		config.StdinOnce = false
 	}
 
-	// Disable sigProxy when in TTY mode
-	if config.Tty {
-		opts.sigProxy = false
-	}
-
 	// Telling the Windows daemon the initial size of the tty during start makes
 	// a far better user experience rather than relying on subsequent resizes
 	// to cause things to catch up.