Background and goal

With the work in T331403 on removing line-height-heading legacy token in products completed, it's time to remove it in Codex and from skin variables.

Acceptance criteria

• Remove line-height-heading in Codex Actually not happening as we keep all legacy tokens that are unchanged value in WikimediaUI Base in 'deprecated-aliases-wikimedia-ui.json' until we can get rid of it altogether.
• Remove it in MediaWiki core