Delete behaviours folder and tidy up views

[aaaaargZombies]

User story

As a developer I need remove old code that we no longer use so that other work can continue unimpeded.

Acceptance criteria

• Passing tests
• PR Refactor image preview on upload field in partner admin in stimulus #1424 should already be merged
• views should not contain <div class="behavior-trigger" data-behavior="user.form"></div> etc
• behaviours js files and related imports removed

Implementation notes & questions

This would break select2 inputs on "collections" but this part of the site has been abandoned.

It will resolve the following individual issues: #1419, #1420, #1422 but will avoid writing more repetitive tickets.

Implementation plan

• Remove class and data bindings from views
• Remove imports from admin.js
• Delete behaviors folder.