driver/docker-container: remove conditional UsernsMode=host for userns

This special handling was added in 5f8600f,
to work around an issue in the daemon. That issue was fixed in [moby@a826ca3],
which was backported to docker v20.10.13 in [moby@660b996].

Given that docker 20.10 reached EOL, and any currently supported version
of docker would have the fix from [moby@a826ca3], we can remove this special
handling.

[moby@a826ca3]: moby/moby@a826ca3
[moby@660b996]: moby/moby@660b996

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

Author: thaJeztah

driver/docker-container/driver.go

@@ -25,7 +25,6 @@ import (
 	"github.com/docker/docker/api/types/image"
 	"github.com/docker/docker/api/types/mount"
 	"github.com/docker/docker/api/types/network"
-	"github.com/docker/docker/api/types/system"
 	"github.com/docker/docker/pkg/jsonmessage"
 	"github.com/docker/docker/pkg/stdcopy"
 	"github.com/moby/buildkit/client"
@@ -207,17 +206,6 @@ func (d *Driver) create(ctx context.Context, l progress.SubLogger) error {
 					hc.CgroupParent = d.cgroupParent
 				}
 			}
-
-			secOpts, err := system.DecodeSecurityOptions(info.SecurityOptions)
-			if err != nil {
-				return err
-			}
-			for _, f := range secOpts {
-				if f.Name == "userns" {
-					hc.UsernsMode = "host"
-					break
-				}
-			}
 		}
 		_, err := d.DockerAPI.ContainerCreate(ctx, cfg, hc, &network.NetworkingConfig{}, nil, d.Name)
 		if err != nil && !cerrdefs.IsConflict(err) {