storaged: read emmc health data from sysfs

Sysfs data is straightforward so we don't need parsing anymore.

Also removed periodical check since data is set only once during
driver initialization. Checking at every device boot or storaged
restart should be sufficient to monitor long term status change.

Test: adb logcat -d -b events | grep storaged_emmc_info
Bug: 36228467
Change-Id: I2a181f52c9f19de1e679a3a905aaebafe4d08227