wait(1);
if(mouse_left){ent_create("bullet.mdl",my.pos,move_bullet_func);wait(5);
}

You know what this does? It creates a bullet every 5 ticks, and those are alot of bullets in one second. More than your current entity limit (max_entities) which causes that error.

And you should declare your functions with parantheses behind them:
function blabla() {
}

Probably doesn't solve your non-removing bullets problem, but fix this first.