cleanup function to preserve /data/media
fix f2fs conversion of /data on /data/media devices
cleanup useless code:

reset_ext4fs_info() is always called by make_ext4fs()
formatting
fix null struct exception
Allow restoring ext4 backup to f2fs filesystem, vice versa

- if backup image and target partition have different fstype and both are either f2fs or ext4, preserve target partition fstype
- this makes it possible to migrate your backups from one system to another by manually formatting target partition to a different fstype

adapted from @kumajaya
6.43.3