Remove "@ingroup themeable" from all Classy templates

Problem/Motivation

From https://www.drupal.org/node/1354#templates:

Do not include @ingroup themeable in overridden template files in a theme -- only in the base version. Otherwise, theme-specific versions are documented the same way.

You could interpret "the base version" as from a base theme, but it's referring to the default output which (usually) comes from a module.

One of the reasons why we want to remove these lines from Classy's templates is so that Classy's templates won't be listed here as duplicates:

https://api.drupal.org/api/drupal/core%21modules%21system%21theme.api.ph...

Proposed resolution

Remove all the @ingroup themeable lines (and preceding blank line) from Classy's .html.twig templates.

Example before/after code from Classy's page.html.twig:

Before:

 * @see template_preprocess_page()
 * @see html.html.twig
 *
 * @ingroup themeable
 */
#}

After:

 * @see template_preprocess_page()
 * @see html.html.twig
 */
#}

Remaining tasks

• Create patch
• Review patch

Beta phase evaluation

User interface changes

n/a

API changes

n/a