Migrate Channelstore categories to sqlx (#19506)

Remove db:"-" tags from model.Channel as well.

```release-note
NONE
```

model/channel.go

@@ -51,11 +51,11 @@ type Channel struct {
 	ExtraUpdateAt     int64                  `json:"extra_update_at"`
 	CreatorId         string                 `json:"creator_id"`
 	SchemeId          *string                `json:"scheme_id"`
-	Props             map[string]interface{} `json:"props" db:"-"`
+	Props             map[string]interface{} `json:"props"`
 	GroupConstrained  *bool                  `json:"group_constrained"`
 	Shared            *bool                  `json:"shared"`
 	TotalMsgCountRoot int64                  `json:"total_msg_count_root"`
-	PolicyID          *string                `json:"policy_id" db:"-"`
+	PolicyID          *string                `json:"policy_id"`
 	LastRootPostAt    int64                  `json:"last_root_post_at"`
 }