The Wall Street community is not anxious to celebrate the second anniversary of the collapse of Lehman Brothers, other than to signify that a significant amount of time has passed since one of its darkest hours. It wishes the news media, and the public, would forget the excesses that led to the near-collapse of the financial world. But investors can’t afford to forget, because there are too many lessons that came to light in the crisis, and which are more easily seen and remembered today. As the anniversary passes quietly this year, here are six lessons investors should revisit…