Remove the empty instance folder when exiting the identity dialog

collect_app/src/main/java/org/odk/collect/android/activities/FormFillingActivity.java

@@ -558,6 +558,7 @@ private void setupViewModels(FormEntryViewModelFactory formEntryViewModelFactory
 
         identityPromptViewModel.isFormEntryCancelled().observe(this, isFormEntryCancelled -> {
             if (isFormEntryCancelled) {
+                identityPromptViewModel.exit();
                 exit();
             }
         });

collect_app/src/main/java/org/odk/collect/android/formentry/audit/IdentityPromptViewModel.java

@@ -9,6 +9,7 @@
 import androidx.lifecycle.ViewModel;
 
 import org.odk.collect.android.javarosawrapper.FormController;
+import org.odk.collect.android.utilities.FileUtils;
 
 public class IdentityPromptViewModel extends ViewModel {
 
@@ -20,6 +21,7 @@ public class IdentityPromptViewModel extends ViewModel {
 
     private String identity = "";
     private String formName;
+    private String instanceFolder;
 
     public IdentityPromptViewModel() {
         updateRequiresIdentity();
@@ -28,6 +30,7 @@ public IdentityPromptViewModel() {
     public void formLoaded(@NonNull FormController formController) {
         this.formName = formController.getFormTitle();
         this.auditEventLogger = formController.getAuditEventLogger();
+        this.instanceFolder = formController.getInstanceFile().getParent();
         updateRequiresIdentity();
     }
 
@@ -72,4 +75,8 @@ private static boolean userIsValid(String user) {
     public String getFormTitle() {
         return formName;
     }
+
+    public void exit() {
+        FileUtils.purgeMediaPath(instanceFolder);
+    }
 }