Silicon Valley Bank is known for serving venture capital firms and the local tech startups those firms invested in. On Wednesday, the bank announced a bunch of bad news. It sold almost all of its securities, some $21 billion worth, at a $1.8 billion loss because deposits dropped quickly. The bank said this was because VC-funded companies were burning cash faster than it expected — at exactly the time when VC funding has slowed. To fill the hole in the balance sheet, the bank tried to sell…