Deprecating Activity Finder 3.x branch. We have it in 4.x branch for upgrade needs

[podarok]

Original Issue, this PR is going to fix: https://openy.atlassian.net/browse/MAINTAIN-74

Make sure these boxes are checked before asking for review of your pull request - thank you!

If there is a new feature or this is a bug fix - use 9.x-2.x branch. We'll tag for release if the bug is critical asap or tag for release next bug fix release until critical issue arrived.

Steps for review

• Ensure there is no v3 available in composer.json.
• Check docs update in AF Deprecate v3 openy_activity_finder#60

General checks

• All coding styles are fulfilled and there are no any issues reported by CodeSniffer. See Code of Conduct.
• Documentation has been updated according to PR changes.
• Steps for review have been provided according to PR changes.
  
• Make sure you've provided all necessary hook_update_N to support upgrade path.
• Make sure your git email is associated with account on drupal.org, otherwise you won't get commits there.
  
• If you would like to get credits on drupal.org, check documentation.

Thank you for your contribution!

[gundevel]

Build comment file:

Check Open Y Installation Wizard at http://install.openy.cibox.tools/build3181/install.php

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[gundevel]

Open Y Upgrade Path site check installed at http://upgrade.openy.cibox.tools/build3181/

[gundevel]

Build comment file:

Check Open Y Installation Wizard at http://install.openy.cibox.tools/build3229/install.php

---

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
http://openy.cibox.tools:8080/job/PR_BUILDER_COMPOSER/3229/

[gundevel]

Open Y Upgrade Path site check installed at http://upgrade.openy.cibox.tools/build3229/