customizer.js: Remove a workaround for older less.js.

BS3 commits: f3077ee424316e79b2c78874c79dec6442134b03
Use variables for breadcrumb padding

BS3 commits: bdd0890c0f076f6f3c008de2884e53d581f142d1
Fixes 11837: grid containers are fixed width now, no longer max-width

BS3 commits: a3a2525124cacae7c94a9280066cbe6eb6524059