Fix `Relation#delete_all` inconsistency

We were generating this configuration with :json what may break
applications upgrating from Rails 4.0-.

Now we always generate with a safer value and people is free to choose
hybrid if they want.

We don't generate with hybrid by default because there are some cases
that can fail. These cases are explained on the upgrading guide.

Closes #15141.

Remove unecessary require

Remove the assignment for real this time.

cc:
https://github.com/rails/rails/commit/a11e2fcff8cdc9691b977d8330abe63024f8c732#commitcomment-6353614
and 0369dbfd

We are using that code path in only one place so we should not add a
conditional to all the other cases. This will avoid performance
regressions on the old paths.

Small refactoring on clear_transaction_record_state

Remove code related to adapter which are no longer in repo

Allow custom asset host to be passed in asset_url

As we have remove code for these adapters so no need to have tasks

Document conflicts in `db/schema.rb` [ci skip]

fixed a typo

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

Make sure when we clean the `@_start_transaction_state` var we do it in
the same code-path.
Also this makes `clear_transaction_record_state`, more consistent with `restore_transaction_record_state`

fixes stack level too deep exception on action named 'status' rendering 'head :ok'

Add RFC 4791 MKCALENDAR method

Changed extract_limit in class Column to return correct mysql float and
double limits

This reverts commit 5d2d3010.

Remove unused method in RouteSet test.

Follow up to #15109.

/cc @Gaurav2728

/cc @yahonda

The bit of URL generation that is optimized is the generation of
the path so things like :host, :port, etc. are irrelevant.