Remove needless quote

[syohex]

This fixes the following byte-compile warning.

ox-hugo.el:443:12: Warning: defcustom for
    ‘org-hugo-export-with-section-numbers’ has syntactically odd type
    ‘'(choice (const :tag Don't number only in body 'onlytoc) (const :tag
    Don't number any heading nil) (const :tag Number all headings t) (integer
    :tag Number to level))’

[kaushalmodi]

@syohex Thank you! I haven't seen this warning before: probably because I am still using Emacs 28.1.50?

[syohex]

I haven't seen this warning before: probably because I am still using Emacs 28.1.50?

I suppose that this warning occurs since Emacs 29.0.50