[lldb] Remove unused ThreadPlan tracer utilities (NFC)

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

lldb/include/lldb/Target/Thread.h

@@ -1052,10 +1052,6 @@ public:
 
   void RestoreThreadStateFromCheckpoint(ThreadStateCheckpoint &saved_state);
 
-  void EnableTracer(bool value, bool single_step);
-
-  void SetTracer(lldb::ThreadPlanTracerSP &tracer_sp);
-
   // Get the thread index ID. The index ID that is guaranteed to not be re-used
   // by a process. They start at 1 and increase with each new thread. This
   // allows easy command line access by a unique ID that is easier to type than

lldb/include/lldb/Target/ThreadPlanStack.h

@@ -48,10 +48,6 @@ public:
 
   void ThreadDestroyed(Thread *thread);
 
-  void EnableTracer(bool value, bool single_stepping);
-
-  void SetTracer(lldb::ThreadPlanTracerSP &tracer_sp);
-
   void PushPlan(lldb::ThreadPlanSP new_plan_sp);
 
   lldb::ThreadPlanSP PopPlan();

lldb/include/lldb/Target/ThreadPlanTracer.h

@@ -50,14 +50,6 @@ public:
 
   bool TracingEnabled() { return m_enabled; }
 
-  bool EnableSingleStep(bool value) {
-    bool old_value = m_single_step;
-    m_single_step = value;
-    return old_value;
-  }
-
-  bool SingleStepEnabled() { return m_single_step; }
-  
   Thread &GetThread();
 
 protected:
@@ -71,7 +63,6 @@ protected:
 private:
   bool TracerExplainsStop();
 
-  bool m_single_step;
   bool m_enabled;
   lldb::StreamSP m_stream_sp;
   Thread *m_thread;

lldb/source/Target/Thread.cpp

@@ -1180,14 +1180,6 @@ Status Thread::QueueThreadPlan(ThreadPlanSP &thread_plan_sp,
   return status;
 }
 
-void Thread::EnableTracer(bool value, bool single_stepping) {
-  GetPlans().EnableTracer(value, single_stepping);
-}
-
-void Thread::SetTracer(lldb::ThreadPlanTracerSP &tracer_sp) {
-  GetPlans().SetTracer(tracer_sp);
-}
-
 bool Thread::DiscardUserThreadPlansUpToIndex(uint32_t plan_index) {
   // Count the user thread plans from the back end to get the number of the one
   // we want to discard:

lldb/source/Target/ThreadPlan.cpp

@@ -156,8 +156,7 @@ bool ThreadPlan::OkayToDiscard() {
 }
 
 lldb::StateType ThreadPlan::RunState() {
-  if (m_tracer_sp && m_tracer_sp->TracingEnabled() &&
-      m_tracer_sp->SingleStepEnabled())
+  if (m_tracer_sp && m_tracer_sp->TracingEnabled())
     return eStateStepping;
   else
     return GetPlanRunState();

lldb/source/Target/ThreadPlanStack.cpp

@@ -124,20 +124,6 @@ void ThreadPlanStack::ThreadDestroyed(Thread *thread) {
   }
 }
 
-void ThreadPlanStack::EnableTracer(bool value, bool single_stepping) {
-  for (ThreadPlanSP plan : m_plans) {
-    if (plan->GetThreadPlanTracer()) {
-      plan->GetThreadPlanTracer()->EnableTracing(value);
-      plan->GetThreadPlanTracer()->EnableSingleStep(single_stepping);
-    }
-  }
-}
-
-void ThreadPlanStack::SetTracer(lldb::ThreadPlanTracerSP &tracer_sp) {
-  for (ThreadPlanSP plan : m_plans)
-    plan->SetThreadPlanTracer(tracer_sp);
-}
-
 void ThreadPlanStack::PushPlan(lldb::ThreadPlanSP new_plan_sp) {
   // If the thread plan doesn't already have a tracer, give it its parent's
   // tracer:

lldb/source/Target/ThreadPlanTracer.cpp

@@ -35,11 +35,11 @@ using namespace lldb_private;
 
 ThreadPlanTracer::ThreadPlanTracer(Thread &thread, lldb::StreamSP &stream_sp)
     : m_process(*thread.GetProcess().get()), m_tid(thread.GetID()),
-      m_single_step(true), m_enabled(false), m_stream_sp(stream_sp) {}
+      m_enabled(false), m_stream_sp(stream_sp) {}
 
 ThreadPlanTracer::ThreadPlanTracer(Thread &thread)
     : m_process(*thread.GetProcess().get()), m_tid(thread.GetID()),
-      m_single_step(true), m_enabled(false), m_stream_sp() {}
+      m_enabled(false), m_stream_sp() {}
 
 Stream *ThreadPlanTracer::GetLogStream() {
   if (m_stream_sp)
@@ -75,7 +75,7 @@ void ThreadPlanTracer::Log() {
 }
 
 bool ThreadPlanTracer::TracerExplainsStop() {
-  if (m_enabled && m_single_step) {
+  if (m_enabled) {
     lldb::StopInfoSP stop_info = GetThread().GetStopInfo();
     return (stop_info->GetStopReason() == eStopReasonTrace);
   } else