Revert "initramfs-live-install*: fix the "install" boot option"

This patch causes install to fail because /etc/mtab doesn't exist, so revert it
for now until the root problem is fixed.

[ YOCTO #4501 ]

This reverts commit 2f5d41f94c53aaf606de66891c37de0dbd86f54b.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>