chore: remove anon user when sign up with a new user (#4253)

* chore: remove anon user when sign up with a new user

* chore: clippy

Author: appflowy

frontend/appflowy_flutter/integration_test/cloud/anon_user_continue_test.dart

@@ -56,14 +56,14 @@ void main() {
 
       // tap the continue as anonymous button
       await tester
-          .tapButton(find.text(LocaleKeys.signIn_continueAnonymousUser.tr()));
+          .tapButton(find.text(LocaleKeys.signIn_loginStartWithAnonymous.tr()));
       await tester.expectToSeeHomePage();
 
-      // assert the name of the anon user is local_user
+      // New anon user name
       await tester.openSettings();
       await tester.openSettingsPage(SettingsPage.user);
       final userNameInput = tester.widget(userNameFinder) as UserNameInput;
-      expect(userNameInput.name, 'local_user');
+      expect(userNameInput.name, 'Me');
     });
   });
 }

frontend/rust-lib/flowy-user/src/manager.rs

@@ -415,6 +415,7 @@ impl UserManager {
         self
           .migrate_anon_user_data_to_cloud(&old_user, &new_user, authenticator)
           .await?;
+        self.remove_anon_user();
         let _ = self.database.close(old_user.session.user_id);
       }
     }

frontend/rust-lib/flowy-user/src/services/historical_user.rs

@@ -40,6 +40,10 @@ impl UserManager {
     let _ = self.store_preferences.set_object(ANON_USER, session);
   }
 
+  pub fn remove_anon_user(&self) {
+    self.store_preferences.remove(ANON_USER);
+  }
+
   pub async fn get_anon_user(&self) -> FlowyResult<UserProfilePB> {
     let anon_session = self
       .store_preferences