Remove special treatment of contrib modules

I've updated the IP with the list of projects that need to be informed and also a list of legacy components that will also be removed in that context.

MR!667 removes the legacy stuff.

MR!668 removes support for the autosave module. No related issue is being created because that module is no longer maintained.

MR!669 removes support for the chosen module.

MR!670 removes support for the ckeditor 4 module. No related issue is being created because that module is no longer maintained.

MR!671 removes support for the coffee module.

MR!672 removes support for the dropzonejs module.

MR!673 removes support for the entity_browser module.

MR!674 removes support for the entity_reference_layout module. No related issue is being created because that module is no longer maintained.

MR!675 removes support for the inline_entity_form module.

MR!676 removes support for the layout_paragraphs module.

MR!676 removes support for the linkit module.

MR!678 removes support for the module_filter module.

MR!679 removes support for the paragraphs module.

MR!680 removes support for the responsive_preview module.

MR!680 removes support for the term_reference_tree module.

MR!682 removes support for the upgrade_status module.

MR!683 removes support for the webform module.

MR!684 removes support for the workbench module.

MR!685 removes support for the classy theme.

All contrib code is being removed.