Swift: remove Binding<> class

That class was meant to allow aggregate initialization of generated
C++ entries having the label `id` as first argument.

As aggregate initialization turned out to be undesirable (names of
fields are not explicit, and `{}` must be inserted for empty
superclasses), this commit removes it and disallows aggregate
initialization altogether by defining empty constructors for generated
classes.

swift/extractor/trap/TrapLabel.h

@@ -58,11 +58,6 @@ inline auto trapQuoted(const std::string& s) {
   return std::quoted(s, '"', '"');
 }
 
-template <typename Tag>
-struct Binding {
-  TrapLabel<Tag> id;
-};
-
 }  // namespace codeql
 
 namespace std {