Convert recovery.fstab to the "version 2" format.

This is what the ZIP creation tool (ota_from_target_files) expects since
our recovery advertises that it uses recovery.fstab version 2.

Change-Id: Ie47576f8cc4c78d33072ae9a7c2acd7e563b77d1
Convert the changes from common-ota_from_target_files.py to a device-specific hook for the "core" ota_from_target_files script.

This removes lots of duplicate code.
Remove the custom variant of the "ota_from_target_files" script.

This was converted to the device-specific hook concept so those copied
files are not required anymore.