[lldb] Call ThreadPlan::DiscardPlan from Thread::DiscardPlan

[kastiglione]

Summary

Correct Thread::DiscardPlan to call DiscardPlan instead of PopPlan.

lldb/source/Target/Thread.cpp

 //===-- Thread.cpp --------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "lldb/Target/Thread.h"
 #include "lldb/Breakpoint/BreakpointLocation.h"
 #include "lldb/Core/Debugger.h"
 #include "lldb/Core/FormatEntity.h"
 #include "lldb/Core/Module.h"
 #include "lldb/Core/StructuredDataImpl.h"
 #include "lldb/Core/ValueObject.h"
 #include "lldb/Host/Host.h"
 #include "lldb/Interpreter/OptionValueFileSpecList.h"
void Thread::PopPlan() {
   if (log) {
     LLDB_LOGF(log, "Popping plan: \"%s\", tid = 0x%4.4" PRIx64 ".",
               popped_plan_sp->GetName(), popped_plan_sp->GetThread().GetID());
   }
 }
 
 void Thread::DiscardPlan() {
   Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_STEP));
-  ThreadPlanSP discarded_plan_sp = GetPlans().PopPlan();
+  ThreadPlanSP discarded_plan_sp = GetPlans().DiscardPlan();
 
   LLDB_LOGF(log, "Discarding plan: \"%s\", tid = 0x%4.4" PRIx64 ".",
             discarded_plan_sp->GetName(), 
             discarded_plan_sp->GetThread().GetID());
 }
 
 void Thread::AutoCompleteThreadPlans(CompletionRequest &request) const {
   const ThreadPlanStack &plans = GetPlans();