Remove FileVarDecl and BlockVarDecl. They are replaced by VarDecl::isBlockVarDecl() and VarDecl::isFileVarDecl().

This is a fairly mechanical/large change. As a result, I avoided making any changes/simplifications that weren't directly related. I did break two Analysis tests. I also have a couple FIXME's in UninitializedValues.cpp. Ted, can you take a look? If the bug isn't obvious, I am happy to dig in and fix it (since I broke it).

llvm-svn: 49748