remove notification as requested in PLT-6537 (#6412)

app/notification.go

@@ -98,9 +98,11 @@ func SendNotifications(post *model.Post, team *model.Team, channel *model.Channe
 		if len(potentialOtherMentions) > 0 {
 			if result := <-Srv.Store.User().GetProfilesByUsernames(potentialOtherMentions, team.Id); result.Err == nil {
 				outOfChannelMentions := result.Data.([]*model.User)
+				if channel.Type != model.CHANNEL_GROUP {
 					go sendOutOfChannelMentions(sender, post, team.Id, outOfChannelMentions)
 				}
 			}
+		}
 
 		// find which users in the channel are set up to always receive mobile notifications
 		for _, profile := range profileMap {