Remove leftover shortcodes

[robwent]

This is related to issue #493

The clean_string function seems to be used before some plugins have registered their shortcodes, so they don't get rendered by do_shortcode and are left in the description.

This removes anything within square brackets that are left in the description without removing the inner content (Using strip_shortcodes removes inner content).

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[robwent]

Also related to #977

[rawdreeg]

Thanks for contributing.

The issue is addressed by #2254, so I will close this PR