staging: android: persistent_ram: Remove never used struct persistent_ram_zone members

Remove 'old_log_footer_size' and 'early' members of struct
persistent_ram_zone, as these were never used at all.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>