switch off brightness reduction

this was added due to a recommendation from MrF (HUB75)  but it seems to work without, too.

wled00/bus_manager.cpp

@@ -885,7 +885,7 @@ uint32_t BusHub75Matrix::getPixelColor(uint16_t pix) const {
 
 void BusHub75Matrix::setBrightness(uint8_t b, bool immediate) {
   _bri = b;
-  if (_bri > 238) _bri=238;
+  // if (_bri > 238) _bri=238; // not strictly needed. Enable this line if you see glitches at highest brightness.
   display->setBrightness(_bri);
 }