Migrate Reactions store to Sync by default (#10737)

* Migrate Reactions store to Sync by default

* Fixing tests

* Fixing tests

* Fixing govet

* fixing tests

* Addressing PR review comments

app/export.go

@@ -407,15 +407,14 @@ func (a *App) buildPostReplies(postId string) (*[]ReplyImportData, *model.AppErr
 func (a *App) BuildPostReactions(postId string) (*[]ReactionImportData, *model.AppError) {
 	var reactionsOfPost []ReactionImportData
 
-	result := <-a.Srv.Store.Reaction().GetForPost(postId, true)
-	if result.Err != nil {
-		return nil, result.Err
+	reactions, err := a.Srv.Store.Reaction().GetForPost(postId, true)
+	if err != nil {
+		return nil, err
 	}
 
-	reactions := result.Data.([]*model.Reaction)
-
 	for _, reaction := range reactions {
-		user, err := a.Srv.Store.User().Get(reaction.UserId)
+		var user *model.User
+		user, err = a.Srv.Store.User().Get(reaction.UserId)
 		if err != nil {
 			return nil, err
 		}