Most of the biggest exits for venture-backed companies in the Bay Area in the third quarter came from IPOs. That's probably no surprise in a year when the number of companies going public from the region has already more than doubled last year's total and is closing in on a 10-year high. Only three of the top 10 exits came in sales of VC-backed businesses, with one of those M&A deals coming just before the acquired company was planning to make its Wall Street debut. Making the top 10 for the quarter…