if you need to remove only matching (), your code won't do. Since '.' will match any character including ')' and since it is a greedy match, it will only eliminate the outmost parenthesis and (!)everything in between. Also the space before the parenthesis would have to match. You could use

s/\([^)]*\)//g  #eliminate anything in parenthesis
   or
s/\(([^)]*)\)/$1/g #remove matching parens but not the content
[download]

but you would have to repeat that regex until no match was found anymore. Except if you only have only one level of parenthesis, then one execution of the regex would be enough

removing characters can be done with one regex using a character class:

s/[%*()]//g;
[download]

even parenthesis if you don't mind that they don't match

you could simply use + instead of {1,}

UPDATE to correct a very silly mistake indeed: changed ? to +