Fixed duplicate subscribers in ActiveSupport::Subscriber

ActiveSupport::Subscriber no longer creates multiple subscribers when
you redefine a method.
Fix `Relation#delete_all` inconsistency

When relation scopes include one of `uniq`, `group`, `having` or
`offset`, the generated query ignores them and that causes unintended
records to be deleted. This solves the issue by restricting the deletion
when those scopes are present.

rails/rails#11985
Merge pull request #15071 from leafac/issues/11985

Fix `Relation#delete_all` inconsistency
Add CHANGELOG entry for #15071 [ci skip]
Merge pull request #15037 from roccoblues/fix_duplicate_activesupport_subscribers

Fixed duplicate subscribers in ActiveSupport::Subscriber

Conflicts:
	activesupport/CHANGELOG.md
Replace first person point of view on guides.

[skip ci]
Merge pull request #15143 from htanata/first_person_pronouns

Replace first person point of view on guides.