Other minor fixes to remove unused headers and correct some comments

[siddimore]

Summary

This PR applies a small set of non-invasive fixes in the C++ SDK.
All changes are documentation/comment corrections or include hygiene improvements, with no intended runtime behavior changes.

Changes

• Changed RemoteTrackPublication to LocalTrackPublication in the constructor note.
• Removed empty private section in remote_video_track.h
• Removed unused iostream include from track.h
  This avoids unnecessarily pulling a heavy standard header through a widely included public header.
• Fixed VideoStream usage example in video_stream.h
  Updated sample snippet to use VideoStream types and symbols instead of AudioStream names.
• Removed unused include in remote_audio_track.cpp
• Removed unused include in remote_video_track.cpp

Notes

No functional logic was changed.
No API signatures were changed.
Changes are limited to comments, examples, access-section cleanup, and unused includes.