Adapt recovery fstab files usage for Android 4.3

As explained here:
https://source.android.com/devices/tech/storage/config.html
since Android 4.3 fstab files have been unified all using the same syntax.
This commit drops the now useless recovery.fstab file and uses
fstab.boundary also for recovery, making it work again.

Signed-off-by: Diego Rondini <diego.rondini@kynetics.it>