Fix exception when closing XML file during conversion of OPI to BOB

The code was refactored to use auto-closing therefore the file does
not need to be explictly closed.

Author: rjwills28

app/display/model/src/main/java/org/csstudio/display/builder/model/Converter.java

@@ -175,7 +175,6 @@ private void convert(final File infile, final File outfile) throws Exception {
 				final ModelReader reader = new ModelReader(new FileInputStream(infile));
 				DisplayModel model = reader.readModel();
 				writer.writeModel(model);
-				writer.close();
 			} catch (Exception e) {
 				throw e;
 			}