fix(cloud_firestore): remove get-write validation (#2919)

* fix(cloud_firestore): remove get-write validation

* remove invalid test

Author: Ehesp

packages/cloud_firestore/cloud_firestore_platform_interface/lib/src/method_channel/method_channel_transaction.dart

@@ -26,20 +26,11 @@ class MethodChannelTransaction extends TransactionPlatform {
         FirebaseFirestorePlatform.instanceFor(app: Firebase.app(appName));
   }
 
-  int _documentGetCount = 0;
-
   List<Map<String, dynamic>> _commands = [];
 
   /// Returns all transaction commands for the current instance.
-  ///
-  /// All get operations must be written, otherwise an [AssertionError] will be thrown
   @override
   List<Map<String, dynamic>> get commands {
-    if (_documentGetCount > 0) {
-      assert(_documentGetCount <= _commands.length,
-          "All transaction get operations must also be written.");
-    }
-
     return _commands;
   }
 
@@ -58,7 +49,6 @@ class MethodChannelTransaction extends TransactionPlatform {
       'transactionId': _transactionId,
       'reference': _firestore.doc(documentPath),
     });
-    _documentGetCount++;
 
     return DocumentSnapshotPlatform(
       _firestore,

packages/cloud_firestore/cloud_firestore_platform_interface/test/method_channel_tests/method_channel_transaction_test.dart

@@ -64,11 +64,6 @@ void main() {
     });
 
     group('commands', () {
-      test('should throw if get is not written', () async {
-        await transaction.get(mockDocumentReference.path);
-        expect(() => transaction.commands, throwsAssertionError);
-      });
-
       test('returns with equal checks', () async {
         await transaction.get(mockDocumentReference.path);
         transaction.set(mockDocumentReference.path, {'foo': 'bar'});