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

ref:
https://github.com/CyanogenMod/android_bootable_recovery/commit/534ae75afa96a784bec4d14a98972e64ffb2101d
https://github.com/CyanogenMod/android_bootable_recovery/commit/e0d1d69c04f14ccd59eb06751ae1b9b7af05ac4d