Only skip frames for local unwinds.

When doing a remote unwind, and there is a crash in the unwind stack
code or in libbacktrace, the old version would skip those frames.
This makes debugging crashes in those libraries a bit difficult.

Bug: 68820611

Test: Ran unit tests.
Test: kill -3 a zygote process and verify no frames in
Test: libunwindstack.so/libbacktrace.so.
Test: Forced a crash in libunwindstack.so and verified the tombstone
Test: contains the full crash.
Change-Id: I297e5b3775c87c0dddf57ebb423bd72ba1baf193