debuggerd: remove the raw stack dump.

This takes a lot of space, isn't convincingly useful, and makes it
likely that the far more valuable stuff that comes after it gets
truncated. So let's just drop it.

Bug: http://b/139860930
Test: manual crasher, presubmit
Change-Id: Ie417ffc07e3cb17e95fdb3d183f8c87de0f34b89