LibJS: Remove Interpreter::declare_variable()

Since declarations are now hoisted and handled on scope entry, the job
of a VariableDeclaration becomes to actually initialize variables.

As such, we can remove the part where we insert variables into the
nearest relevant scope. Less work == more speed! :^)

Libraries/LibJS/AST.cpp

@@ -828,7 +828,6 @@ void UpdateExpression::dump(int indent) const
 Value VariableDeclaration::execute(Interpreter& interpreter) const
 {
  for (auto& declarator : m_declarations) {
- interpreter.declare_variable(declarator.id().string(), m_declaration_kind);
  if (auto* init = declarator.init()) {
  auto initalizer_result = init->execute(interpreter);
  if (interpreter.exception())

Libraries/LibJS/Interpreter.cpp

@@ -122,27 +122,6 @@ void Interpreter::exit_scope(const ScopeNode& scope_node)
  m_unwind_until = ScopeType::None;
 }
 
-void Interpreter::declare_variable(const FlyString& name, DeclarationKind declaration_kind)
-{
- switch (declaration_kind) {
- case DeclarationKind::Var:
- for (ssize_t i = m_scope_stack.size() - 1; i >= 0; --i) {
- auto& scope = m_scope_stack.at(i);
- if (scope.type == ScopeType::Function) {
- scope.variables.set(move(name), { js_undefined(), declaration_kind });
- return;
- }
- }
-
- global_object().put(move(name), js_undefined());
- break;
- case DeclarationKind::Let:
- case DeclarationKind::Const:
- m_scope_stack.last().variables.set(move(name), { js_undefined(), declaration_kind });
- break;
- }
-}
-
 void Interpreter::set_variable(const FlyString& name, Value value, bool first_assignment)
 {
  for (ssize_t i = m_scope_stack.size() - 1; i >= 0; --i) {

Libraries/LibJS/Interpreter.h

@@ -96,7 +96,6 @@ class Interpreter {
 
  Optional<Value> get_variable(const FlyString& name);
  void set_variable(const FlyString& name, Value, bool first_assignment = false);
- void declare_variable(const FlyString& name, DeclarationKind);
 
  void gather_roots(Badge<Heap>, HashTable<Cell*>&);