Do not read the EMMC ext_csd register from dumpstate

The code to read mmcblk0 ext_csd register from debugfs is being removed
from dumpstate for the following reasons.

1. From Android R, platform code cannot access debugfs nodes since its
ABI is considered unstable.

2. Not all devices use EMMC and hence the right place to read this
register is actually the dumpstate HAL if required(perhaps using the
MMC_IOC_CMD ioctl that provides a way to read the ext_csd register).

Test: make
Bug: 134669095

Change-Id: Ie79d87e95ba718182a8be48b02973cca3eab13bb