tp: remove over-cautious detection of use-after-free in iterators

Back in the very old days of trace processor, we introduced a mechanism
to detect using an iterator after the trace processor instance was
freed. Unfortunately, turns out there are two problems:
1. The implementation is buggy. This is because iterators don't inform
   the trace processor when they are moved so addresses the trace
   processor holds onto are invalid.
2. Trace processor instances are very long lived in practice so the
   likelihood that someone holds iterators past the lifetime is
   unlikely.

Most other C++ classes don't try and protect against use-after-frees and
instead just crash so follow their behaviour given the unlikeliness of
ever hitting this scenario.

Change-Id: Ie37e0c746b7541d2fbec9adacd4ad9bc8194f406