Make ListenerRegistration::Cleanup delegate to Remove.

Not entirely sure why it wasn't done before. This prevents the problem where `FirestoreInternal` might be holding on to invalid (already deleted) `ListenerRegistration`s after cleanup.

SKIP_FIRESTORE_KOKORO_BUILD_TEST

PiperOrigin-RevId: 298664884

Author: var-const

firestore/src/android/firestore_android.cc

@@ -233,8 +233,11 @@ FirestoreInternal::~FirestoreInternal() {
 
   {
     MutexLock lock(listener_registration_mutex_);
-    for (ListenerRegistrationInternal* registration : listener_registrations_) {
-      delete registration;
+    // TODO(varconst): investigate why not all listener registrations are
+    // cleared.
+    // FIREBASE_ASSERT(listener_registrations_.empty());
+    for (auto* reg : listener_registrations_) {
+      delete reg;
     }
     listener_registrations_.clear();
   }

firestore/src/common/listener_registration.cc

@@ -99,10 +99,7 @@ void ListenerRegistration::Remove() {
 }
 
 void ListenerRegistration::Cleanup() {
-  delete internal_;
-  internal_ = nullptr;
-  // `ListenerRegistration` additionally holds a pointer to `FirestoreInternal`,
-  // which must also be set to null.
+  Remove();
   firestore_ = nullptr;
 }
 

firestore/src/ios/firestore_ios.cc

@@ -10,6 +10,7 @@
 #include "firestore/src/ios/credentials_provider_ios.h"
 #include "firestore/src/ios/document_reference_ios.h"
 #include "firestore/src/ios/document_snapshot_ios.h"
+#include "firestore/src/ios/hard_assert_ios.h"
 #include "firestore/src/ios/listener_ios.h"
 #include "absl/memory/memory.h"
 #include "absl/types/any.h"
@@ -56,7 +57,12 @@ FirestoreInternal::FirestoreInternal(
   ApplyDefaultSettings();
 }
 
-FirestoreInternal::~FirestoreInternal() { ClearListeners(); }
+FirestoreInternal::~FirestoreInternal() {
+  std::lock_guard<std::mutex> lock(listeners_mutex_);
+  HARD_ASSERT_IOS(listeners_.empty(),
+                  "Expected all listeners to be unregistered by the time "
+                  "FirestoreInternal is destroyed.");
+}
 
 std::shared_ptr<api::Firestore> FirestoreInternal::CreateFirestore(
     App* app, std::unique_ptr<CredentialsProvider> credentials) {