Remove unused test class (#6907)

app/src/androidTest/java/de/danoeh/antennapod/core/service/download/StubDownloader.java

@@ -1,54 +0,0 @@
-package de.danoeh.antennapod.core.service.download;
-
-import androidx.annotation.NonNull;
-import androidx.core.util.Consumer;
-import de.danoeh.antennapod.model.download.DownloadResult;
-import de.danoeh.antennapod.net.download.serviceinterface.DownloadRequest;
-
-public class StubDownloader extends Downloader {
-
-    private final long downloadTime;
-
-    @NonNull
-    private final Consumer<DownloadResult> onDownloadComplete;
-
-    public StubDownloader(@NonNull DownloadRequest request, long downloadTime,
-                          @NonNull Consumer<DownloadResult> onDownloadComplete) {
-        super(request);
-        this.downloadTime = downloadTime;
-        this.onDownloadComplete = onDownloadComplete;
-    }
-
-    @Override
-    protected void download() {
-        try {
-            Thread.sleep(downloadTime);
-        } catch (Throwable t) {
-            t.printStackTrace();
-        }
-        onDownloadComplete.accept(result);
-    }
-
-    @NonNull
-    @Override
-    public DownloadRequest getDownloadRequest() {
-        return super.getDownloadRequest();
-    }
-
-    @NonNull
-    @Override
-    public DownloadResult getResult() {
-        return super.getResult();
-    }
-
-    @Override
-    public boolean isFinished() {
-        return super.isFinished();
-    }
-
-    @Override
-    public void cancel() {
-        super.cancel();
-        result.setCancelled();
-    }
-}