recovery: remove prefer tar (this has been made the default behavior)

ref:
https://github.com/CyanogenMod/android_bootable_recovery/commit/7322ac1f328a4b5916e4641ce55ab924d3b7ecee
https://github.com/CyanogenMod/android_bootable_recovery/commit/50f5fb001f7781b621322c0330fd61407fa79e28

Change-Id: I2b5280cd10fca0302c2baa03a61f25f6880e4037