Fix links to design.gitlab.com pages

doc/development/fe_guide/dropdowns.md

 ---
-redirect_to: 'https://design.gitlab.com/components/dropdowns/'
+redirect_to: 'https://design.gitlab.com/components/dropdown/'
 ---

doc/development/fe_guide/frontend_faq.md

@@ -69,7 +69,7 @@ banner on top of the component examples indicates that:
 > component.
 
 For example, at the time of writing, this type of warning can be observed for
-[all form components](https://design.gitlab.com/components/forms/). It, however,
+[all form components](https://design.gitlab.com/components/form/). It, however,
 doesn't imply that the component should not be used.
 
 GitLab always asks to use `<gl-*>` components whenever a suitable component exists.