*: deprecate --pivot-root and hide it runc --help

Existing users will still be able to use it, but new users won't be
tempted into using this flag (and their containers should be able to run
without issue without this flag anyway).

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

Author: cyphar

create.go

@@ -44,8 +44,9 @@ command(s) that get executed on start, edit the args parameter of the spec. See
 			Usage: "specify the file to write the process id to",
 		},
 		cli.BoolFlag{
-			Name:  "no-pivot",
-			Usage: "do not use pivot root to jail process inside rootfs to work around limitations when running in an initramfs (this option is deprecated, insecure, and unnecessary now that pivot_root works with initramfs -- see <https://github.com/opencontainers/runc/issues/4435>)",
+			Name:   "no-pivot",
+			Usage:  "(deprecated; do not use)",
+			Hidden: true,
 		},
 		cli.BoolFlag{
 			Name:  "no-new-keyring",

run.go

@@ -57,8 +57,9 @@ command(s) that get executed on start, edit the args parameter of the spec. See
 			Usage: "disable the use of the subreaper used to reap reparented processes",
 		},
 		cli.BoolFlag{
-			Name:  "no-pivot",
-			Usage: "do not use pivot root to jail process inside rootfs to work around limitations when running in an initramfs (this option is deprecated, insecure, and unnecessary now that pivot_root works with initramfs -- see <https://github.com/opencontainers/runc/issues/4435>)",
+			Name:   "no-pivot",
+			Usage:  "(deprecated; do not use)",
+			Hidden: true,
 		},
 		cli.BoolFlag{
 			Name:  "no-new-keyring",