Fix orphaned transient timeout cleanup

[teams4evolve]

Trac ticket: https://core.trac.wordpress.org/ticket/65863

When the transient value row is missing, delete_transient() currently
does not remove the corresponding timeout row.

This changes delete_transient() and delete_site_transient() to always
attempt to delete their timeout rows.

Added regression tests covering orphaned transient timeout rows.

Tests:

• vendor/bin/phpunit tests/phpunit/tests/option/transient.php
• vendor/bin/phpunit tests/phpunit/tests/option/siteTransient.php
• PHPCS passed for the changed files.

[github-actions]

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[github-actions]

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