A couple of alternate options here - any of such can simply only resolve to making the intentions clear, although it's hardly an issue.
It might be a little clearer, albeit not much, using
String withoutLastComma = result.substring(0, result.lastIndexOf(","));
Or just refactor a little, which could be more explanatory:
StringBuilder result = new StringBuilder();
for (int i = 0; i < paramList.size(); i++)
if (i + 1 != paramList.size())
Or, lastly, use a string utility library as linked in other answers provided; though, the thought of doing so brings the term 'sledgehammer to crack a nut' to mind, but it might well be justified depending on what other operations you require to carry out.