Delete unused `EnableTracer()` and `SetTracer()` functions on `Thread`. By deleting
these, their `ThreadPlan` counterparts also become unused.
Then, by deleting `ThreadPlanStack::EnableTracer`, `EnableSingleStep` becomes unused.
With no more callers to `EnableSingleStep`, the value `m_single_step` is always true and
can be removed as well.
Differential Revision: https://reviews.llvm.org/D96666
that were not reported by the OS plugin. To facilitate this, move
adding/updating the ThreadPlans for a Thread to the ThreadPlanStackMap.
Also move dumping thread plans there as well.
Added some tests for "thread plan list" and "thread plan discard" since
I didn't seem to have written any originally.
Differential Revision: https://reviews.llvm.org/D76814
Dave Lee