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 @@ public:
 
     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*>&);