Change all uintptr_t to uint64_t in API.

In order to support the offline unwinding properly, get rid of the
usage of non-fixed type uintptr_t from all API calls.

In addition, completely remove the old local and remote unwinding code
that used libunwind.

The next step will be to move the offline unwinding to the new unwinder.

Bug: 65682279

Test: Ran unit tests for libbacktrace/debuggerd.
Test: Ran debuggerd -b on a few arm and arm64 processes.
Test: Ran crasher and crasher64 and verified tombstones look correct.
Change-Id: Ib0c6cee3ad6785a102b74908a3d8e5e93e5c6b33