Remove dm-verity from boot image

dm-verity

Credit: thohac@xda

I took the tools/arm/magiskboot from that git and did it manually.

Here are my steps.
put magiskboot in /data/local/bin
chmod +x /data/local/bin/magiskboot.
put unpacked boot.img on the device and patch with magisk. rename back to boot.img

mkdir unpacked; cd unpacked #make a working dir and switch to it
magiskboot unpack ../boot.img #unpack the image
magiskboot dtb dtb patch #use magiskboot to patch dtb
magiskboot --cpio ramdisk.cpio 'extract fstab.qcom fstab.qcom' #unpack fstab.qcom from ramdisk
edit fstab.qcom and remove avb entries #I hope someone in this forum has the regex skill to come up with a sed for this
magiskboot cpio ramdisk.cpio 'add 0440 fstab.qcom fstab.qcom' #replace the one on the ramdisk
magiskboot repack ../boot.img new-boot.img