Change the way tombstones are added to dropbox.

Use the proto tombstone as source of truth and ignore the text
tombstone. Instead create the text tombstone by omitting the memory data
from the proto tombstone to save space on data that would get removed
anyway. This allows us to save bandwidth and avoid truncating useful
data from the tombstones.

Test: atest BootReceiverTest
Bug: 296207744

Change-Id: I809122d3206ce326cbbbceadb45c3b98b9762a3e