tracing: fix -Wunused-private-field warning

Remove `external_buffer_` from `InternalTraceBuffer` as it seems not to
be used anywhere.

PR-URL: https://github.com/nodejs/node/pull/10416
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

src/tracing/node_trace_buffer.cc

@@ -4,10 +4,9 @@ namespace node {
 namespace tracing {
 
 InternalTraceBuffer::InternalTraceBuffer(size_t max_chunks, uint32_t id,
-    NodeTraceWriter* trace_writer, NodeTraceBuffer* external_buffer)
+                                         NodeTraceWriter* trace_writer)
     : flushing_(false), max_chunks_(max_chunks),
-      trace_writer_(trace_writer), external_buffer_(external_buffer),
-      id_(id) {
+      trace_writer_(trace_writer), id_(id) {
   chunks_.resize(max_chunks);
 }
 
@@ -90,8 +89,8 @@ void InternalTraceBuffer::ExtractHandle(
 NodeTraceBuffer::NodeTraceBuffer(size_t max_chunks,
     NodeTraceWriter* trace_writer, uv_loop_t* tracing_loop)
     : tracing_loop_(tracing_loop), trace_writer_(trace_writer),
-      buffer1_(max_chunks, 0, trace_writer, this),
-      buffer2_(max_chunks, 1, trace_writer, this) {
+      buffer1_(max_chunks, 0, trace_writer),
+      buffer2_(max_chunks, 1, trace_writer) {
   current_buf_.store(&buffer1_);
 
   flush_signal_.data = this;

src/tracing/node_trace_buffer.h

@@ -20,8 +20,7 @@ class NodeTraceBuffer;
 class InternalTraceBuffer {
  public:
   InternalTraceBuffer(size_t max_chunks, uint32_t id,
-                      NodeTraceWriter* trace_writer,
-                      NodeTraceBuffer* external_buffer);
+                      NodeTraceWriter* trace_writer);
 
   TraceObject* AddTraceEvent(uint64_t* handle);
   TraceObject* GetEventByHandle(uint64_t handle);
@@ -44,7 +43,6 @@ class InternalTraceBuffer {
   bool flushing_;
   size_t max_chunks_;
   NodeTraceWriter* trace_writer_;
-  NodeTraceBuffer* external_buffer_;
   std::vector<std::unique_ptr<TraceBufferChunk>> chunks_;
   size_t total_chunks_ = 0;
   uint32_t current_chunk_seq_ = 1;