PLT-8233: Purge ChannelMemberHistory Data when Data Retention Job runs (#7937)

* Changed the channel member history purge function to match pattern established by other data retention purge methods

* Simplifying the channel member history store and associated tests

* Regenerating mocks

* Using a constant

store/store.go

@@ -165,7 +165,7 @@ type ChannelMemberHistoryStore interface {
 	LogJoinEvent(userId string, channelId string, joinTime int64) StoreChannel
 	LogLeaveEvent(userId string, channelId string, leaveTime int64) StoreChannel
 	GetUsersInChannelDuring(startTime int64, endTime int64, channelId string) StoreChannel
-	PurgeHistoryBefore(time int64, channelId string) StoreChannel
+	PermanentDeleteBatch(endTime int64, limit int64) StoreChannel
 }
 
 type PostStore interface {