Remove @todo-comment linking to closed issue in \settings_tray_install

Problem/Motivation

In #3123832: [META] Fix @todo items referencing closed issues we discovered that there's a @todo in \settings_tray_install which references a d.o. issue that is already closed: #2783791: Module install doesn't invalidate render cache.

Here's the @todo:

  // This module affects the rendering of blocks and of the page.
  // @todo Remove in https://www.drupal.org/node/2783791.
  Cache::invalidateTags(['rendered']);

Steps to reproduce

Proposed resolution

#2783791: Module install doesn't invalidate render cache was marked as Closed (cannot reproduce). Although the approach in #2783791-40: Module install doesn't invalidate render cache might still be valid nowadays, the issue lost track years ago, so it looks like there's not much community interest.

Besides that several Core module install hooks have the mentioned line of (Cache::invalidateTags(['rendered']);), so there's no need to mark the install hook of the settings_tray one as special

I think we can safely remove the @todo lines from the settings_tray_install hook.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet