This reverts commit 41b8ecd6.

Unbreak upgrades from OpenWrt 19.07 (Gluon 2021.1.x) by undoing the
partition table change.

It should be noted that the EFI images generated by OpenWrt are slightly
smaller than the non-EFI images for some reason (due to a smaller gap
between the boot and root partitions), so upgrading a VM created using a
Gluon 2023.1 (EFI) image to a newer non-EFI image will truncate the root
partition.

Linux will warn about the truncation on boot ("sda: p2 size 212992 extends
beyond EOD, truncated"), but it doesn't cause any other issues, as the
root partitions of x86 squashfs images are mostly empty, and the overlay
is created in the actual available space after the upgrade. The cosmetic
issue will go away as soon as we switch to EFI again (likely with Gluon
2023.2).

Closes #2967