Removes unused debug code

It's not used for a long long time.

lib/TerminalDisplay.cpp

@@ -1122,11 +1122,6 @@ void TerminalDisplay::updateImage()
   char *dirtyMask = new char[columnsToUpdate+2];
   QRegion dirtyRegion;
 
-  // debugging variable, this records the number of lines that are found to
-  // be 'dirty' ( ie. have changed from the old _image to the new _image ) and
-  // which therefore need to be repainted
-  int dirtyLineCount = 0;
-
   for (y = 0; y < linesToUpdate; ++y)
   {
     const Character*       currentLine = &_image[y*this->_columns];
@@ -1220,8 +1215,6 @@ void TerminalDisplay::updateImage()
     // then this line must be repainted.
     if (updateLine)
     {
-        dirtyLineCount++;
-
         // add the area occupied by this line to the region which needs to be
         // repainted
         QRect dirtyRect = QRect( _leftMargin+tLx ,