Remove unused AV helper fixtures from e10a2531

Several fixtures for helpers are removed. They were introduced in
ActionView by @strzalek but never referenced in any test.
Remove HelperyTestHelper not used in any test

HelperyTestHelper was introduced in 66ef922 by @josevalim
to pair with HelperyTestController. This test controller was
later removed in e10a253 by @strzalek, leaving HelperyTestHelper unused
Merge pull request #12231 from harshadsabne/master

[ci skip] Update plugins.md
[ci skip] Consistency wording of 9.6 in form_helpers.md

Chapter 9 is giving a user and set of addresses example.
So 'Add a new address' would be more consistent.
Also change the javascript to JavaScript.
Merge pull request #12239 from JuanitoFatas/form_helpers

[ci skip] Consistency wording of 9.6 in form_helpers.md
surplus : in attachment_fu plugin

surplus ':' character in url
incorrect urls 

I've found two incorrects urls for adding ':' at the end of the url
incorrect url

incorrect url
Removes unused code related to DatabaseTasks.
Merge pull request #12245 from kennyj/remove_no_using_code_20130916

Removes unused code related to DatabaseTasks.
[ci skip] Improve readability of 4.3's NOTE in migration.md.
Merge pull request #12011 from jetthoughts/11963_fix_join_with_association_scope

Collapse where constraints to the Arel::Nodes::And node

Conflicts:
	activerecord/CHANGELOG.md
Merge pull request #12250 from JuanitoFatas/migration

[ci skip] Improve readability of 4.3's NOTE in migration.md.
Fix Show link on resource
`skiping` => `skipping`
Remove tzinfo dependency from Action Pack

This gem is used by Active Support but it should not be a dependency of
Action Pack.
Merge pull request #12262 from sferik/remove_tzinfo_from_actionpack

Remove tzinfo dependency from Action Pack
There's no need to do this

AS does the following inside Time.find_zone! ...
`ActiveSupport::TimeZone[time_zone] || TZInfo::Timezone.get(time_zone)`
and given that the test is stubbing AS::TZ[] we don't need the removed
code.
Fix an issue where router can't recognize downcased url encoding path.
Add params option for button_to

The parameters are rendered as hidden form fields within the generated
form. This is useful for when a record has multiple buttons associated
with it, each of which target the same controller method, but which
need to submit different attributes.