message: Update grfmt_pxm.cpp
  remove comment in .ppm
diff: @@ -466,11 +466,9 @@ bool PxMEncoder::write(const Mat& img, const std::vector<int>& params)
  // write header;
  const int code = ((mode == PXM_TYPE_PBM) ? 1 : (mode == PXM_TYPE_PGM) ? 2 : 3)
  + (isBinary ? 3 : 0);
  - const char* comment = "# Generated by OpenCV " CV_VERSION "\n";
  - int header_sz = sprintf(buffer, "P%c\n%s%d %d\n",
  - (char)('0' + code), comment,
  - width, height);
  + int header_sz = sprintf(buffer, "P%c\n%d %d\n",
  + (char)('0' + code), width, height);
  CV_Assert(header_sz > 0);
  if (mode != PXM_TYPE_PBM)
  {
  