[lldb] Delete TestBacktraceAll.py

This test is completely nondeterministic, environment-dependent and does
not test what it was supposed to test (reverting the associated patch
does not make it fail).

I tried to figure out what the patch was meant to fix to see if I can
create a better test with the current tools, but I was not able to
understand the problem (it sounds like it has something to do with local
classes, but I don't understand the details).