ipq806x: tr4400v2: revert nesting of MTD partitions that bricks device

ipq806x: tr4400v2: revert nesting of MTD partitions that bricks device

This reverts commit e1043a746a1030062e73ea027d9a35c58bce6c6a, that
attempts to nest partitions that overlap but are not nested. This
causes the 'ubi' partition to be truncated, making rootfs inaccessible
and bricking the device.

Also, had this commit worked, it would have renumbered MTD partitions
in a way that would have broken documented scripts for installation and
update of main and recovery OSes, making backups, return to stock, etc,
and broken user configurations that put the 'extra' partition to use.

Signed-off-by: Rodrigo Balerdi <lanchon@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/16944
Signed-off-by: Robert Marko <robimarko@gmail.com>