Use default destructor and remove unnecessary virtual destructor
Use default destructor and remove unnecessary virtual destructor

Only the virtual destructor in the base class is needed, and can use the
default.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@263335 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm