do not run a gc after creating a plot

the gc often takes a second or more, which slows down the rendering a
lot

pdb-ui/src/main/java/org/lucares/pdbui/PdbController.java

@@ -88,7 +88,6 @@ public class PdbController implements HardcodedValues {
 				final String imageUrl = WEB_IMAGE_OUTPUT_PATH + "/"
 						+ result.getImageName();
 				LOGGER.trace("image url:  {}", imageUrl);
-				System.gc();
 				
 				return new PlotResponse(
 						DataSeries.toMap(result.getDataSeries()), imageUrl);