package/tini: restore use as docker-init

Commit 24cac9c4e6a36fd14b263a8eecf7ae7d58ab5a59 "system: add tini as
init system" made BR2_PACKAGE_TINI depend on BR2_INIT_TINI. This is
incorrect: tini is not only needed when building a container image
using Buildroot, but also to run Docker containers on Buildroot
systems using another another init system, if Docker is configured to
provide an init process for the container (e.g. with "docker run
--init"). The tini package already provides the "docker-init" symlink
required for that.

Example error without tini installed:

$ docker run --rm -ti --init alpine
docker: Error response from daemon: exec: "docker-init": executable file not found in $PATH.

Signed-off-by: Fiona Klute (WIWA) <fiona.klute@gmx.de>
Reviewed-by: Christian Stewart <christian@aperture.us>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/tini/Config.in

@@ -1,7 +1,6 @@
 config BR2_PACKAGE_TINI
 	bool "tini"
 	depends on BR2_USE_MMU # fork()
-	depends on BR2_INIT_TINI
 	help
 	  tini is a simple but valid init binary to
 	  act as PID 1 for containers.