Revert "Add docker exec run a command in privileged mode"

This reverts commit 72a500e9e5929b038816d8bd18d462a19e571c99.

Signed-off-by: Jessica Frazelle <princess@docker.com>

Conflicts:
	daemon/execdriver/native/exec.go
	integration-cli/docker_cli_exec_test.go
	runconfig/exec.go