Fix to marketing iframe middle-click href: course does not always have openable url.

lms/templates/courseware/mktg_course_about.html

@@ -53,9 +53,7 @@
           %endif
         %elif allow_registration:
         <a class="action action-register register ${'has-option-verified' if len(course_modes) > 1 else ''}"
-            %if user.is_authenticated():
-                href="${reverse('about_course', args=[course.id.to_deprecated_string()])}"
-            %else:
+            %if not user.is_authenticated():
                 href="${reverse('register_user')}?course_id=${course.id | u}&enrollment_action=enroll"
             %endif
         >${_("Enroll in")} <strong>${course.display_number_with_default | h}</strong>