Port `SnapshotVersion` for the rest Firestore modulo (#1185)

* remove conversions in `Local` and `Remote`

* replace `FSTSnapshotVersion` in `Model`

* replace `FSTSnapshotVersion` in the rest

* let test check equal with C++ equal

* fix newly added code

* address changes

1 files changed, 5 insertions, 5 deletions

diff --git a/Firestore/Source/Local/FSTLocalSerializer.mm b/Firestore/Source/Local/FSTLocalSerializer.mm
index 652fa5f..8fa1278 100644
--- a/Firestore/Source/Local/FSTLocalSerializer.mm
+++ b/Firestore/Source/Local/FSTLocalSerializer.mm
@@ -103,8 +103,8 @@ using firebase::firestore::model::SnapshotVersion;
   FSTSerializerBeta *remoteSerializer = self.remoteSerializer;
 
   FSTObjectValue *data = [remoteSerializer decodedFields:document.fields];
-  const DocumentKey key = [remoteSerializer decodedDocumentKey:document.name];
-  const SnapshotVersion version = [remoteSerializer decodedVersion:document.updateTime];
+  DocumentKey key = [remoteSerializer decodedDocumentKey:document.name];
+  SnapshotVersion version = [remoteSerializer decodedVersion:document.updateTime];
   return [FSTDocument documentWithData:data key:key version:version hasLocalMutations:NO];
 }
 
@@ -122,8 +122,8 @@ using firebase::firestore::model::SnapshotVersion;
 - (FSTDeletedDocument *)decodedDeletedDocument:(FSTPBNoDocument *)proto {
   FSTSerializerBeta *remoteSerializer = self.remoteSerializer;
 
-  const DocumentKey key = [remoteSerializer decodedDocumentKey:proto.name];
-  const SnapshotVersion version = [remoteSerializer decodedVersion:proto.readTime];
+  DocumentKey key = [remoteSerializer decodedDocumentKey:proto.name];
+  SnapshotVersion version = [remoteSerializer decodedVersion:proto.readTime];
   return [FSTDeletedDocument documentWithKey:key version:version];
 }
 
@@ -188,7 +188,7 @@ using firebase::firestore::model::SnapshotVersion;
 
   FSTTargetID targetID = target.targetId;
   FSTListenSequenceNumber sequenceNumber = target.lastListenSequenceNumber;
-  const SnapshotVersion version = [remoteSerializer decodedVersion:target.snapshotVersion];
+  SnapshotVersion version = [remoteSerializer decodedVersion:target.snapshotVersion];
   NSData *resumeToken = target.resumeToken;
 
   FSTQuery *query;