Might want to lower the temps a little got a fan in there? should be alright, your not using nutes are you?
No need to clip the leaves, they will fall off when they are dead. What is more important is to find out what happened because other than the cotyledons you shouldnt have dying leaves on a three week old plant.
A 25 day old auto should be showing its first signs of flowering. Autos start flowering at around day 21. Your plant sounds stunted. Because autos skip the vegetative stage and go straight into flowering, they don't have enough time to recover from any stress introduced before it flowers and this affects the size, and of course, the yield. You should post pictures so we can tell how big/small it is. If it's as small as you mentioned then it's stunted, and if I were you I'd start over. But post pictures if you want to be sure. (Remember to include something for size reference)