Refactor: Remove unused field

CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/zip/CityGmlZipArchive.java

@@ -25,7 +25,6 @@ public class CityGmlZipArchive implements Serializable {
     private List<CityGmlZipEntry> entries;
     private final Path archivePath;
     private final String archiveNameRE;
-    private ZipFile zipFile;
 
     public static CityGmlZipArchive fromZipFile(String zipFile, ParserConfiguration config) {
         CityGmlZipArchive archive = CityGmlZipArchive.register(zipFile);
@@ -57,14 +56,11 @@ public class CityGmlZipArchive implements Serializable {
 
     public void mountArchive(ParserConfiguration config){
         try (ZipFile zip = new ZipFile(archivePath.toFile())) {
-            zipFile = zip;
             for (CityGmlZipEntry entry : entries){
                 entry.loadEntry(config);
             }
         } catch (IOException e) {
             logger.error(e);
-        } finally {
-            zipFile = null;
         }
     }