Remove gl-new-card CSS

What does this MR do and why?

Removes unsed gl-new-card classes as we have migrated all instances to either Crud or back to a regular Card. See also Migration: GlCard (gl-new-card variant) to Crud (#476988)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

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Related to #452231 (closed) Closing Migration: GlCard (gl-new-card variant) to Crud (#476988)