LibJS: Move ordinary_call_bind_this() to ECMAScriptFunctionObject

Now that it only needs to deal with ECMAScriptFunctionObject via
internal_call() / internal_construct(), we can:

- Remove the generic FunctionObject parameter
- Move it from the VM to ECMAScriptFunctionObject
- Make it private

Userland/Libraries/LibJS/Runtime/VM.h

@@ -274,9 +274,6 @@ public:
     void save_execution_context_stack();
     void restore_execution_context_stack();
 
-    // TODO: Move these elsewhere once only used for ECMAScriptFunctionObject.
-    void ordinary_call_bind_this(FunctionObject&, ExecutionContext&, Value this_argument);
-
 private:
     explicit VM(OwnPtr<CustomData>);