Prevent [Withdrawn] duplication in page titles

[AshGDS]

What / Why

• Some work was done to simplify page title code recently, including handling [Withdrawn] in titles. But sometimes the content item title already has [Withdrawn], so it can get duplicated. This introduces a guard to prevent this happening.
• For example, on production https://www.gov.uk/government/publications/face-coverings-when-to-wear-one-and-how-to-make-your-own/face-coverings-when-to-wear-one-and-how-to-make-your-own has [Withdrawn] [Withdrawn] in the title.

[AshGDS]

Closing as @sairamya93 had made a PR first without me realising! #5289