Remove unnecessary virtual dtor.
Remove unnecessary virtual dtor.

This class doesn't have virtual member functions, and no instances
of this class is deleted through base pointers.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@299581 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld