ENGR00268442 mmc: remove the boot partition access codes on 3.0.35

ENGR00268442 mmc: remove the boot partition access codes on 3.0.35

Regarding to the following community commit, remove all the boot
partition access codes added before.
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371a689f64b0da140c3bcd3f55305ffa1c3a58ef
mmc: MMC boot partitions support.

Allows device MMC boot partitions to be accessed. MMC partitions are
treated effectively as separate block devices on the same MMC card.
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Boot partition access howto:
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To enable write access to /dev/mmcblkXbootY, disable the forced
read-only access with:

echo 0 > /sys/block/mmcblkXbootY/force_ro

To re-enable read-only access:

echo 1 > /sys/block/mmcblkXbootY/force_ro
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Signed-off-by: Richard Zhu <r65037@freescale.com>