You are advocating building small patterns so that they can be combined into larger patterns, right? If so, your code is buggy (and I don't mean just the superfluous (?:)).

>perl -E"$sqr=qr/\[.*?\]/; $_='ab[cd]ef[gh]'; s/$sqr$//; say"
ab
[download]

Fixed:

>perl -E"$sqr=qr/\[[^\[\]]*\]/; $_='ab[cd]ef[gh]'; s/$sqr$//; say"
ab[cd]ef
[download]