Removing Controller::getRequest() deprecation note

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | --
| License       | MIT
| Doc PR        | not yet :angel: 

Hi guys!

When the `request_stack` was introduced, we deprecated `Controller::getRequest()` - #9553.

I would argue that there *is* value to this method, as it saves me from needing to add a `use` statement in my controller to get the request. This is similar to why we have the `redirect` shortcut method.

Since the method *does* use the `request_stack`, I don't see the disadvantage to having this.

Thanks!