Revert "Merge pull request #27636 from mtsmfm/disable-referential-integrity-without-superuser-privilege-take-2"

This reverts commit c1faca63, reversing
changes made to 8c658a0e.

See https://github.com/rails/rails/pull/27636#issuecomment-297534129

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Ensure bin/yarn matches the one generated by webpacker

Mixin `CollectionProxy::DelegateExtending` after `ClassSpecificRelation`

`respond_to_missing?` should be private

Fix MigratorTest#test_migrator_verbosity

Add `ActiveRecord::Migration.verbose = true`
to be sure that verbose is turned on in the test.

Related to #28865

Ask for a sane version of SDoc

Replace \Z to \z

Remove checks for Enumerator#size method

Fix typos [ci skip]

'lookup' is the noun. 'to look up' is the verb. Looked it up just to
be sure.

cf.
https://en.wiktionary.org/wiki/lookup
https://en.wiktionary.org/wiki/look_up

The Enumerator#size method was introduced in Ruby 2.0.

These tests were added when Rails 4.1 was current, and Ruby 1.9.3 was
still supported. Since Rails 5 only Ruby >= 2.2.2 is supported, so the
checks are no longer necessary.

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Unify the name of GitHub [ci skip]

Add `form_with_generates_remote_forms` to configuring guide [ci skip]

\Z was a mistake of \z. Replace \Z to \z to prevent newly \Z added.

Follow up of #17148.

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Reads better to use the full word.

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[ci_skip] Fix typo in Rails 5.1 upgrade notes

This will allow me to push a release, including bug fixes,
without having to update Rails everytime.

Import from https://github.com/rails/webpacker/pull/277.

Fixes https://github.com/rails/webpacker/issues/278

Set to `form_with_generates_remote_forms` only when config is explicitly specified

Follow up of 03d3f036.

Some of `respond_to?` were replaced to `respond_to_missing?` in 03d3f036.
But the visibility is still public. It should be private.