Searching "Rule BotSpottedLaserSightsAuto" and editing L4D1 survivors' talker files. (biker_dlc2, manager_dlc2, namvet_dlc2 and teengirl_dlc2.) Next, delete the "Response BotSpottedLaserSightsAuto??? { ... }" and "Rule BotSpottedLaserSightsAuto??? { ... }".

You can also adapt this response like following example so bot survivors of L4D1 could speak their own lines.

Francis' example (biker_dlc2.txt):Please note that these responses are only available for bot survivors. Players still can say "Look this!" when playing L4D1 survivors and spotting a laser sight box.