[lldb] Replace empty ctor en dtor bodies with =default (NFC)

Use = default instead of empty constructor and destructor bodies in the
API layer.
diff --git a/lldb/source/API/SBThreadPlan.cpp b/lldb/source/API/SBThreadPlan.cpp
index f6aaa11..b93c317 100644
--- a/lldb/source/API/SBThreadPlan.cpp
+++ b/lldb/source/API/SBThreadPlan.cpp
@@ -96,7 +96,7 @@
   return LLDB_RECORD_RESULT(*this);
 }
 // Destructor
-SBThreadPlan::~SBThreadPlan() {}
+SBThreadPlan::~SBThreadPlan() = default;
 
 lldb_private::ThreadPlan *SBThreadPlan::get() { return m_opaque_sp.get(); }