Remove outdated code relating to "Expose Title in Manage Display"

✨ [META] Expose Title and other base fields in Manage Display Active will introduce the "normal" mechanism for managing display of title and other base fields then deprecate the old specialist non-standard way. With the major release of D10 we should remove the deprecated code.

Changes required have @todo markers linking to this issue, and are summarised below.

Node template

• Remove label, date, author_name - code can use elements[title] etc.
• Remove page, display_submitted - if title/submitted should not be displayed then the corresponding elements will be missing or generate no markup.
• Remove author_attributes, author_picture - instead the information will be part of the rendered formatter output of elements[uid].
• Remove all process code related to the variables removed from the node template, including template_preprocess_node and rdf_preprocess_node.

Field templates

• Remove all copies of field--node--title.html.twig, field--node--uid.html.twig, field--node--created.html.twig.
• In node_theme remove field__node__XXX.

Once we are using field formatters for the base-field output we don't need these special cases.

Node type

Remove $display_submitted, displaySubmitted(), setDisplaySubmitted(), related form/schema. It is controlled through manage display UI settings instead.

Theme setting

Remove the theme setting features.node_user_picture. Instead this is controlled by a setting on the formatter for the uid field.