spotbugs: Unused public or protected field

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

src/main/java/com/owncloud/android/ui/activity/EditorWebView.java

@@ -53,7 +53,6 @@ public abstract class EditorWebView extends ExternalSiteWebView {
     protected Snackbar loadingSnackbar;
 
     protected String fileName;
-    protected String mimeType;
 
     @BindView(R.id.progressBar2)
     ProgressBar progressBar;