Revert "Adding caching to get channel member (#5518)"

This reverts commit ba028ed74b.

einterfaces/cluster.go

@@ -20,7 +20,6 @@ type ClusterInterface interface {
 	InvalidateCacheForChannelMembersNotifyProps(channelId string)
 	InvalidateCacheForChannelPosts(channelId string)
 	InvalidateCacheForWebhook(webhookId string)
-	InvalidateCacheForChannelMember(channelId string, userId string)
 	Publish(event *model.WebSocketEvent)
 	UpdateStatus(status *model.Status)
 	GetLogs() ([]string, *model.AppError)