Cleanup: remove legacy code and data migration

JavaApp/src/main/java/net/kdt/pojavlaunch/PojavLauncher.java

@@ -37,9 +37,8 @@ public class PojavLauncher {
         Thread.currentThread().setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
 
             public void uncaughtException(Thread t, Throwable th) {
-                Tools.showError(th);
-                // Block this thread from exiting
-                while (true) {}
+                th.printStackTrace();
+                System.exit(1);
             }
         });
 

JavaApp/src/main/java/net/kdt/pojavlaunch/Tools.java

@@ -225,24 +225,7 @@ public final class Tools {
 
         return libStr.toString();
     }
-
-    public static void showError(Throwable e) {
-        showError(e, false);
-    }
-
-    public static void showError(final Throwable e, final boolean exitIfOk) {
-        showError("Error", e, exitIfOk, false);
-    }
-
-    public static void showError(final String title, final Throwable e, final boolean exitIfOk) {
-        showError(title, e, exitIfOk, false);
-    }
-
-    private static void showError(final String title, final Throwable e, final boolean exitIfOk, final boolean showMore) {
-        e.printStackTrace();
-        System.exit(1);
-    }
-
+    
     public static void moveInside(String from, String to) {
         File fromFile = new File(from);
         for (File fromInside : fromFile.listFiles()) {