[lldb-dap] Fix for missing 'raw_string_ostream::flush' removal in ProgressEvent.cpp; addressing #108745 (#114087)

I hope it was missed unintentionally, pushing the same for the review.
Ref: #108745

---------

Co-authored-by: Santhosh Kumar Ellendula <[email protected]>
Co-authored-by: Santhosh Kumar Ellendula <[email protected]>

Author: 3 people

lldb/tools/lldb-dap/ProgressEvent.cpp

@@ -110,7 +110,6 @@ json::Value ProgressEvent::ToJSON() const {
   std::string progress_id_str;
   llvm::raw_string_ostream progress_id_strm(progress_id_str);
   progress_id_strm << m_progress_id;
-  progress_id_strm.flush();
   body.try_emplace("progressId", progress_id_str);
 
   if (m_event_type == progressStart) {