Good catch! Better still: s/[$LEFT_DELIMITER]\Q$chord\E[$RIGHT_DELIMITER]//g

Update: After testing, I'd actually rewrite this as:

$LEFT_DELIMITER = '{[';
$RIGHT_DELIMITER = '}]';

$tempstr = 'This is a string containing [Am]brackets.';
$chord = 'Am';

$tempstr =~ s/[\Q$LEFT_DELIMITER\E]\Q$chord\E[\Q$RIGHT_DELIMITER\E]//;
print $tempstr;
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(note the lack of \ in the delimiter strings).

        - tye (but my friends call me "Tye")