clean_taxonomy_cache() Regenerate hierarchy only when needed

[Chouby]

Removes a useless DB query (made by delete_option()) for non-hierarchical taxonomies when cleaning the taxonomy cache.

Trac ticket: https://core.trac.wordpress.org/ticket/64090

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[github-actions]

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[github-actions]

Hi @Chouby! 👋

Thank you for your contribution to WordPress! 💖

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[github-actions]

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[shail-mehta]

@Chouby Thanks for the PR.

The changes look good.👍

[mukeshpanchal27]

@Chouby Could you please add unit tests?

[mukeshpanchal27]

Nice!