Partition Info: Rework

- Use Android's Environment method instead of hard-coding the paths.
- Remove the SD-Card partition info as we already have them on the main
  Storage settings.

Change-Id: Ia812daa485f6c0295ad7cb44af0b2984e504e5eb
Signed-off-by: Lokesh Chamane <lokesh.c703@gmail.com>